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Search: a131044 -id:a131044
Displaying 1-10 of 14 results found. page 1 2
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A261983 Number of compositions of n such that at least two adjacent parts are equal. +10
49
0, 0, 1, 1, 4, 9, 18, 41, 89, 185, 388, 810, 1670, 3435, 7040, 14360, 29226, 59347, 120229, 243166, 491086, 990446, 1995410, 4016259, 8076960, 16231746, 32599774, 65437945, 131293192, 263316897, 527912140, 1058061751, 2120039885, 4246934012, 8505864640 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,5
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
FORMULA
a(n) ~ 2^(n-1). - Vaclav Kotesovec, Sep 08 2015
a(n) = A011782(n) - A003242(n). - Emeric Deutsch, Jul 03 2020
EXAMPLE
a(5) = 9: 311, 113, 221, 122, 2111, 1211, 1121, 1112, 11111.
From Gus Wiseman, Jul 07 2020: (Start)
The a(2) = 1 through a(6) = 18 compositions:
(1,1) (1,1,1) (2,2) (1,1,3) (3,3)
(1,1,2) (1,2,2) (1,1,4)
(2,1,1) (2,2,1) (2,2,2)
(1,1,1,1) (3,1,1) (4,1,1)
(1,1,1,2) (1,1,1,3)
(1,1,2,1) (1,1,2,2)
(1,2,1,1) (1,1,3,1)
(2,1,1,1) (1,2,2,1)
(1,1,1,1,1) (1,3,1,1)
(2,1,1,2)
(2,2,1,1)
(3,1,1,1)
(1,1,1,1,2)
(1,1,1,2,1)
(1,1,2,1,1)
(1,2,1,1,1)
(2,1,1,1,1)
(1,1,1,1,1,1)
(End)
MAPLE
b:= proc(n, i) option remember; `if`(n=0, 0, add(
`if`(i=j, ceil(2^(n-j-1)), b(n-j, j)), j=1..n))
end:
a:= n-> b(n, 0):
seq(a(n), n=0..40);
MATHEMATICA
Table[Length[Select[Join@@Permutations/@IntegerPartitions[n], MatchQ[#, {___, x_, x_, ___}]&]], {n, 0, 10}] (* Gus Wiseman, Jul 06 2020 *)
b[n_, i_] := b[n, i] = If[n == 0, 0, Sum[If[i == j, Ceiling[2^(n-j-1)], b[n-j, j]], {j, 1, n}]];
a[n_] := b[n, 0];
Table[a[n], {n, 0, 40}] (* Jean-François Alcover, Nov 20 2023, after Alois P. Heinz's Maple code *)
CROSSREFS
Column k=1 of A261981.
Cf. A011782, A262046.
The complement A003242 counts anti-runs.
Sum of positive-indexed terms of row n of A106356.
Row sums of A131044.
The (1,1,1) matching case is A335464.
Strict compositions are A032020.
Compositions with adjacent parts coprime are A167606.
Compositions with equal parts contiguous are A274174.
Cf. A114901, A178470, A242882, A244164, A325534, A335448, A335452.
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 07 2015
STATUS
approved
A373954 Excess run-compression of standard compositions. Sum of all parts minus sum of compressed parts of the n-th integer composition in standard order. +10
40
0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 2, 1, 0, 0, 1, 3, 0, 0, 0, 1, 0, 2, 0, 2, 0, 0, 2, 1, 1, 1, 2, 4, 0, 0, 0, 1, 3, 0, 0, 2, 0, 0, 4, 3, 0, 0, 1, 3, 0, 0, 0, 1, 0, 2, 0, 2, 1, 1, 3, 2, 2, 2, 3, 5, 0, 0, 0, 1, 0, 0, 0, 2, 0, 3, 2, 1, 0, 0, 1, 3, 0, 0, 0, 1, 2, 4, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,8
COMMENTS
The k-th composition in standard order (graded reverse-lexicographic, A066099) is obtained by taking the set of positions of 1's in the reversed binary expansion of k, prepending 0, taking first differences, and reversing again. This gives a bijective correspondence between nonnegative integers and integer compositions.
We define the (run-) compression of a sequence to be the anti-run obtained by reducing each run of repeated parts to a single part. Alternatively, compression removes all parts equal to the part immediately to their left. For example, (1,1,2,2,1) has compression (1,2,1).
LINKS
Table of n, a(n) for n=0..86.
Gus Wiseman, Statistics, classes, and transformations of standard compositions
FORMULA
a(n) = A029837(n) - A373953(n).
EXAMPLE
The excess compression of (2,1,1,3) is 1, so a(92) = 1.
MATHEMATICA
stc[n_]:=Differences[Prepend[Join @@ Position[Reverse[IntegerDigits[n, 2]], 1], 0]]//Reverse;
Table[Total[stc[n]]-Total[First/@Split[stc[n]]], {n, 0, 100}]
CROSSREFS
For length instead of sum we have A124762, counted by A106356.
The opposite for length is A124767, counted by A238279 and A333755.
Positions of zeros are A333489, counted by A003242.
Positions of nonzeros are A348612, counted by A131044.
Compositions counted by this statistic are A373951, opposite A373949.
Compression of standard compositions is A373953.
Positions of ones are A373955.
A037201 gives compression of first differences of primes, halved A373947.
A066099 lists the parts of all compositions in standard order.
A114901 counts compositions with no isolated parts.
A116861 counts partitions by this statistic, by length A116608.
A240085 counts compositions with no unique parts.
A333627 takes the rank of a composition to the rank of its run-lengths.
Cf. A070939, A238130, A238343, A272919, A285981, A333213, A333381, A333382.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jun 27 2024
STATUS
approved
A106351 Triangle read by rows: T(n,k) = number of compositions of n into k parts such that no two adjacent parts are equal. +10
34
1, 1, 0, 1, 2, 0, 1, 2, 1, 0, 1, 4, 2, 0, 0, 1, 4, 7, 2, 0, 0, 1, 6, 9, 6, 1, 0, 0, 1, 6, 15, 14, 3, 0, 0, 0, 1, 8, 21, 24, 15, 2, 0, 0, 0, 1, 8, 28, 46, 30, 10, 1, 0, 0, 0, 1, 10, 35, 66, 68, 30, 4, 0, 0, 0, 0, 1, 10, 46, 100, 119, 76, 24, 2, 0, 0, 0, 0, 1, 12, 54, 138, 204, 168, 69, 14, 1, 0, 0, 0, 0 (list; table; graph; refs; listen; history; text; internal format)
OFFSET
1,5
LINKS
Alois P. Heinz, Rows n = 1..141, flattened
A. Knopfmacher and H. Prodinger, On Carlitz compositions, European Journal of Combinatorics, Vol. 19, 1998, pp. 579-589.
FORMULA
G.f.: 1/(1 - Sum_{k>0} (-1)^(k+1)*x^k*y^k/(1-x^k).
EXAMPLE
T(6,3) = 7 because the compositions of 6 into 3 parts with no adjacent equal parts are 3+2+1, 3+1+2, 2+3+1, 2+1+3, 1+3+2, 1+2+3, 1+4+1.
Triangle begins:
1;
1, 0;
1, 2, 0;
1, 2, 1, 0;
1, 4, 2, 0, 0;
1, 4, 7, 2, 0, 0;
1, 6, 9, 6, 1, 0, 0;
1, 6, 15, 14, 3, 0, 0, 0;
1, 8, 21, 24, 15, 2, 0, 0, 0;
...
MAPLE
b:= proc(n, h, t) option remember;
if n<t then 0
elif n=0 then `if`(t=0, 1, 0)
else add(`if`(h=j, 0, b(n-j, j, t-1)), j=1..n)
fi
end:
T:= (n, k)-> b(n, -1, k):
seq(seq(T(n, k), k=1..n), n=1..15); # Alois P. Heinz, Oct 23 2011
MATHEMATICA
nn=10; CoefficientList[Series[1/(1-Sum[y x^i/(1+y x^i), {i, 1, nn}]), {x, 0, nn}], {x, y}]//Grid (* Geoffrey Critzer, Nov 23 2013 *)
PROG
(PARI)
gf(n, y)={1/(1 - sum(k=1, n, (-1)^(k+1)*x^k*y^k/(1-x^k) + O(x*x^n)))}
for(n=1, 10, my(p=polcoeff(gf(n, y), n)); for(k=1, n, print1(polcoeff(p, k), ", ")); print); \\ Andrew Howroyd, Oct 12 2017
CROSSREFS
Row sums: A003242. Columns 3-6: A106352, A106353, A106354, A106355.
Cf. A131044 (at least two adjacent parts are equal).
T(2n,n) gives A221235.
KEYWORD
nonn,tabl
AUTHOR
Christian G. Bower, Apr 29 2005
STATUS
approved
A348612 Numbers k such that the k-th composition in standard order is not an anti-run, i.e., has adjacent equal parts. +10
32
3, 7, 10, 11, 14, 15, 19, 21, 23, 26, 27, 28, 29, 30, 31, 35, 36, 39, 42, 43, 46, 47, 51, 53, 55, 56, 57, 58, 59, 60, 61, 62, 63, 67, 71, 73, 74, 75, 78, 79, 83, 84, 85, 86, 87, 90, 91, 92, 93, 94, 95, 99, 100, 103, 106, 107, 110, 111, 112, 113, 114, 115, 116 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
First differs from A345168 in lacking 37, corresponding to the composition (3,2,1).
A composition of n is a finite sequence of positive integers summing to n. The k-th composition in standard order (row k of A066099) is obtained by taking the set of positions of 1's in the reversed binary expansion of k, prepending 0, taking first differences, and reversing again.
LINKS
Table of n, a(n) for n=1..63.
EXAMPLE
The terms and corresponding standard compositions begin:
3: (1,1) 35: (4,1,1) 61: (1,1,1,2,1)
7: (1,1,1) 36: (3,3) 62: (1,1,1,1,2)
10: (2,2) 39: (3,1,1,1) 63: (1,1,1,1,1,1)
11: (2,1,1) 42: (2,2,2) 67: (5,1,1)
14: (1,1,2) 43: (2,2,1,1) 71: (4,1,1,1)
15: (1,1,1,1) 46: (2,1,1,2) 73: (3,3,1)
19: (3,1,1) 47: (2,1,1,1,1) 74: (3,2,2)
21: (2,2,1) 51: (1,3,1,1) 75: (3,2,1,1)
23: (2,1,1,1) 53: (1,2,2,1) 78: (3,1,1,2)
26: (1,2,2) 55: (1,2,1,1,1) 79: (3,1,1,1,1)
27: (1,2,1,1) 56: (1,1,4) 83: (2,3,1,1)
28: (1,1,3) 57: (1,1,3,1) 84: (2,2,3)
29: (1,1,2,1) 58: (1,1,2,2) 85: (2,2,2,1)
30: (1,1,1,2) 59: (1,1,2,1,1) 86: (2,2,1,2)
31: (1,1,1,1,1) 60: (1,1,1,3) 87: (2,2,1,1,1)
MATHEMATICA
stc[n_]:=Differences[Prepend[Join@@Position[Reverse[IntegerDigits[n, 2]], 1], 0]]//Reverse;
Select[Range[100], MatchQ[stc[#], {___, x_, x_, ___}]&]
CROSSREFS
Constant run compositions are counted by A000005, ranked by A272919.
Counting these compositions by sum and length gives A131044.
These compositions are counted by A261983.
The complement is A333489, counted by A003242.
The non-alternating case is A345168, complement A345167.
A011782 counts compositions, strict A032020.
A238279 counts compositions by sum and number of maximal runs.
A274174 counts compositions with equal parts contiguous.
A336107 counts non-anti-run permutations of prime factors.
A345195 counts non-alternating anti-runs, ranked by A345169.
For compositions in standard order (rows of A066099):
- Length is A000120.
- Sum is A070939
- Maximal runs are counted by A124767.
- Strict compositions are ranked by A233564.
- Maximal anti-runs are counted by A333381.
- Runs-resistance is A333628.
Cf. A029931, A048793, A106356, A114901, A167606, A178470, A228351, A244164, A262046, A335452, A335464.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Nov 03 2021
STATUS
approved
A357182 Number of integer compositions of n with the same length as their alternating sum. +10
26
1, 1, 0, 0, 1, 3, 1, 4, 6, 20, 13, 48, 50, 175, 141, 512, 481, 1719, 1491, 5400, 4929, 17776, 15840, 57420, 52079, 188656, 169989, 617176, 559834, 2033175, 1842041, 6697744, 6085950, 22139780, 20123989, 73262232, 66697354, 242931321, 221314299, 806516560 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,6
COMMENTS
A composition of n is a finite sequence of positive integers summing to n.
The alternating sum of a sequence (y_1,...,y_k) is Sum_i (-1)^(i-1) y_i.
LINKS
Table of n, a(n) for n=0..39.
EXAMPLE
The a(1) = 1 through a(8) = 6 compositions:
(1) (31) (113) (42) (124) (53)
(212) (223) (1151)
(311) (322) (2141)
(421) (3131)
(4121)
(5111)
MATHEMATICA
ats[y_]:=Sum[(-1)^(i-1)*y[[i]], {i, Length[y]}];
Table[Length[Select[Join@@Permutations/@IntegerPartitions[n], Length[#]==ats[#]&]], {n, 0, 15}]
CROSSREFS
For product instead of length we have A114220.
For sum equal to twice alternating sum we have A262977, ranked by A348614.
For product equal to sum we have A335405, ranked by A335404.
For absolute value we have A357183.
These compositions are ranked by A357184.
The case of partitions is A357189.
A003242 counts anti-run compositions, ranked by A333489.
A011782 counts compositions.
A025047 counts alternating compositions, ranked by A345167.
A124754 gives alternating sums of standard compositions.
A238279 counts compositions by sum and number of maximal runs.
A261983 counts non-anti-run compositions.
A357136 counts compositions by alternating sum.
Cf. A000120, A032020, A070939, A106356, A114901, A131044, A178470, A233564, A242882, A262046, A301987.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 28 2022
EXTENSIONS
a(21)-a(39) from Alois P. Heinz, Sep 29 2022
STATUS
approved
A335548 Number of compositions of n with at least one non-contiguous value. +10
25
0, 0, 0, 0, 1, 4, 10, 28, 68, 159, 350, 770, 1642, 3468, 7218, 14870, 30463, 62044, 125818, 254302, 512690, 1031284, 2071858, 4157214, 8334742, 16699103, 33442208, 66947772, 133986940, 268107104, 536404872, 1073082978, 2146555516, 4293665006, 8588112822 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,6
COMMENTS
Also the number of compositions of n matching the pattern (1,2,1) or (2,1,2).
LINKS
Table of n, a(n) for n=0..34.
FORMULA
a(n) = A011782(n) - A274174(n). - Alois P. Heinz, Jul 09 2020
EXAMPLE
The a(4) = 1 through a(6) = 10 compositions:
(121) (131) (141)
(212) (1131)
(1121) (1212)
(1211) (1221)
(1311)
(2112)
(2121)
(11121)
(11211)
(12111)
MAPLE
b:= proc(n, i, p) option remember; `if`(n=0, p!, `if`(i<1, 0,
add(b(n-i*j, i-1, p+`if`(j=0, 0, 1)), j=0..n/i)))
end:
a:= n-> ceil(2^(n-1))-b(n$2, 0):
seq(a(n), n=0..50); # Alois P. Heinz, Jul 09 2020
MATHEMATICA
Table[Length[Select[Join@@Permutations/@IntegerPartitions[n], Length[Split[#]]>Length[Union[#]]&]], {n, 0, 10}]
(* Second program: *)
b[n_, i_, p_] := b[n, i, p] = If[n == 0, p!, If[i<1, 0,
Sum[b[n-i*j, i-1, p + If[j == 0, 0, 1]], {j, 0, n/i}]]];
a[n_] := Ceiling[2^(n-1)] - b[n, n, 0];
a /@ Range[0, 50] (* Jean-François Alcover, May 21 2021, after Alois P. Heinz *)
CROSSREFS
The complement is A274174.
The version for prime indices is A335460.
Anti-run compositions are A003242.
(1,2,1) and (2,1,2)-matching permutations of prime indices are A335462.
(1,2,1)-matching compositions are A335470.
(1,2,1)-avoiding compositions are A335471.
(2,1,2)-matching compositions are A335472.
(2,1,2)-avoiding compositions are A335473.
Cf. A000670, A001339, A011782, A131044, A261983, A333175, A335451, A335460, A335463.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jul 08 2020
EXTENSIONS
More terms from Alois P. Heinz, Jul 09 2020
STATUS
approved
A357189 Number of integer partitions of n with the same length as alternating sum. +10
25
1, 1, 0, 0, 1, 1, 1, 2, 2, 4, 3, 5, 6, 9, 9, 13, 16, 23, 23, 34, 37, 54, 54, 78, 84, 120, 121, 170, 182, 252, 260, 358, 379, 517, 535, 725, 764, 1030, 1064, 1427, 1494, 1992, 2059, 2733, 2848, 3759, 3887, 5106, 5311, 6946, 7177, 9345, 9701, 12577, 12996, 16788 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,8
COMMENTS
A partition of n is a weakly decreasing sequence of positive integers summing to n.
The alternating sum of a sequence (y_1,...,y_k) is Sum_i (-1)^(i-1) y_i.
LINKS
Table of n, a(n) for n=0..55.
EXAMPLE
The a(4) = 1 through a(13) = 9 partitions:
31 311 42 322 53 333 64 443 75 553
421 5111 432 5221 542 5331 652
531 6211 641 6222 751
51111 52211 6321 52222
62111 7311 53311
711111 62221
63211
73111
7111111
MATHEMATICA
ats[y_]:=Sum[(-1)^(i-1)*y[[i]], {i, Length[y]}];
Table[Length[Select[IntegerPartitions[n], Length[#]==ats[#]&]], {n, 0, 30}]
CROSSREFS
For product equal to sum we have A001055, compositions A335405.
For product instead of length we have A004526, compositions A114220.
The version for compositions is A357182, ranked by A357184.
For sum equal to twice alternating sum we have A357189 (this sequence).
These partitions are ranked by A357486.
The reverse version is A357487, ranked by A357485.
A000041 counts partitions, strict A000009.
A025047 counts alternating compositions.
A103919 counts partitions by alternating sum, full triangle A344651.
A357136 counts compositions by alternating sum, full triangle A097805.
Cf. A051159, A070939, A131044, A262046, A262977, A301987, A357183.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 30 2022
STATUS
approved
A128695 Number of compositions of n with parts in N which avoid the adjacent pattern 111. +10
20
1, 1, 2, 3, 7, 13, 24, 46, 89, 170, 324, 618, 1183, 2260, 4318, 8249, 15765, 30123, 57556, 109973, 210137, 401525, 767216, 1465963, 2801115, 5352275, 10226930, 19541236, 37338699, 71345449, 136324309, 260483548, 497722578, 951030367 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
S. Heubach and T. Mansour, Enumeration of 3-letter patterns in compositions, arXiv:math/0603285 [math.CO], 2006
Gus Wiseman, Sequences counting and ranking compositions by the patterns they match or avoid.
FORMULA
G.f.: 1/(1-Sum(i>=1, x^i*(1+x^i)/(1+x^i*(1+x^i)) ) ).
a(n) ~ c * d^n, where d is the root of the equation Sum_{k>=1} 1/(d^k + 1/(1 + d^k)) = 1, d=1.9107639262818041675000243699745706859615884029961947632387839..., c=0.4993008137128378086219448701860326113802027003939127932922782... - Vaclav Kotesovec, May 01 2014, updated Jul 07 2020
For n>=2, a(n) = A091616(n) + A003242(n). - Vaclav Kotesovec, Jul 07 2020
EXAMPLE
From Gus Wiseman, Jul 06 2020: (Start)
The a(0) = 1 through a(5) = 13 compositions:
() (1) (2) (3) (4) (5)
(1,1) (1,2) (1,3) (1,4)
(2,1) (2,2) (2,3)
(3,1) (3,2)
(1,1,2) (4,1)
(1,2,1) (1,1,3)
(2,1,1) (1,2,2)
(1,3,1)
(2,1,2)
(2,2,1)
(3,1,1)
(1,1,2,1)
(1,2,1,1)
(End)
MAPLE
b:= proc(n, t) option remember; `if`(n=0, 1, add(`if`(abs(t)<>j,
b(n-j, j), `if`(t=-j, 0, b(n-j, -j))), j=1..n))
end:
a:= n-> b(n, 0):
seq(a(n), n=0..40); # Alois P. Heinz, Nov 23 2013
MATHEMATICA
nn=33; CoefficientList[Series[1/(1-Sum[(x^i+x^(2i))/(1+x^i+x^(2i)), {i, 1, nn}]), {x, 0, nn}], x] (* Geoffrey Critzer, Nov 23 2013 *)
Table[Length[Select[Join@@Permutations/@IntegerPartitions[n], !MatchQ[#, {___, x_, x_, x_, ___}]&]], {n, 13}] (* Gus Wiseman, Jul 06 2020 *)
CROSSREFS
Column k=0 of A232435.
Cf. A091616, A232432.
The matching version is A335464.
Contiguously (1,1)-avoiding compositions is A003242.
Contiguously (1,1)-matching compositions are A261983.
Compositions with some part > 2 are A008466
Compositions by number of adjacent equal parts are A106356.
Compositions where each part is adjacent to an equal part are A114901.
Compositions with adjacent parts coprime are A167606.
Compositions with equal parts contiguous are A274174.
Patterns contiguously matched by compositions are A335457.
Patterns contiguously matched by a given partition are A335516.
Cf. A005251, A032020, A131044, A178470, A242882, A333175, A335455.
KEYWORD
nonn
AUTHOR
Ralf Stephan, May 08 2007
STATUS
approved
A357488 Number of integer partitions of 2n - 1 with the same length as alternating sum. +10
19
1, 0, 1, 2, 4, 5, 9, 13, 23, 34, 54, 78, 120, 170, 252, 358, 517, 725, 1030, 1427, 1992, 2733, 3759, 5106, 6946, 9345, 12577, 16788, 22384, 29641, 39199, 51529, 67626, 88307, 115083, 149332, 193383, 249456, 321134, 411998, 527472, 673233, 857539, 1089223, 1380772 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
COMMENTS
A partition of n is a weakly decreasing sequence of positive integers summing to n.
The alternating sum of a sequence (y_1,...,y_k) is Sum_i (-1)^(i-1) y_i.
LINKS
Table of n, a(n) for n=1..45.
FORMULA
a(n) = A357189(2n - 1).
EXAMPLE
The a(1) = 1 through a(7) = 9 partitions:
(1) . (311) (322) (333) (443) (553)
(421) (432) (542) (652)
(531) (641) (751)
(51111) (52211) (52222)
(62111) (53311)
(62221)
(63211)
(73111)
(7111111)
MATHEMATICA
ats[y_]:=Sum[(-1)^(i-1)*y[[i]], {i, Length[y]}];
Table[Length[Select[IntegerPartitions[n], Length[#]==ats[#]&]], {n, 1, 30, 2}]
CROSSREFS
For product equal to sum we have A001055, compositions A335405.
The version for compositions appears to be A222763, odd version of A357182.
These are the odd-indexed terms of A357189, ranked by A357486.
These partitions are ranked by the odd-sum portion of A357485.
Except at the start, alternately adding zeros gives A357487.
A000041 counts partitions, strict A000009.
A025047 counts alternating compositions.
A103919 counts partitions by alternating sum, full triangle A344651.
A357136 counts compositions by alternating sum, full triangle A097805.
Cf. A004526, A051159, A114220, A131044, A262046, A262977, A357183, A357184.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Oct 02 2022
EXTENSIONS
More terms from Alois P. Heinz, Oct 04 2022
STATUS
approved
A357183 Number of integer compositions with the same length as the absolute value of their alternating sum. +10
18
1, 1, 0, 0, 2, 3, 2, 5, 12, 22, 26, 58, 100, 203, 282, 616, 962, 2045, 2982, 6518, 9858, 21416, 31680, 69623, 104158, 228930, 339978, 751430, 1119668, 2478787, 3684082, 8182469, 12171900, 27082870, 40247978, 89748642, 133394708, 297933185, 442628598, 990210110 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,5
COMMENTS
A composition of n is a finite sequence of positive integers summing to n.
The alternating sum of a sequence (y_1,...,y_k) is Sum_i (-1)^(i-1) y_i.
LINKS
Table of n, a(n) for n=0..39.
EXAMPLE
The a(1) = 1 through a(8) = 12 compositions:
(1) (13) (113) (24) (124) (35)
(31) (212) (42) (151) (53)
(311) (223) (1115)
(322) (1151)
(421) (1214)
(1313)
(1412)
(1511)
(2141)
(3131)
(4121)
(5111)
MATHEMATICA
ats[y_]:=Sum[(-1)^(i-1)*y[[i]], {i, Length[y]}];
Table[Length[Select[Join@@Permutations/@IntegerPartitions[n], Length[#]==Abs[ats[#]]&]], {n, 0, 15}]
CROSSREFS
For product instead of length we have A114220.
For sum equal to twice alternating sum we have A262977, ranked by A348614.
For product equal to sum we have A335405, ranked by A335404.
This is the absolute value version of A357182.
These compositions are ranked by A357185.
The case of partitions is A357189.
A003242 counts anti-run compositions, ranked by A333489.
A011782 counts compositions.
A025047 counts alternating compositions, ranked by A345167.
A124754 gives alternating sums of standard compositions.
A238279 counts compositions by sum and number of maximal runs.
A261983 counts non-anti-run compositions.
A357136 counts compositions by alternating sum.
Cf. A000120, A032020, A070939, A106356, A114901, A131044, A178470, A233564, A242882, A262046, A301987.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 28 2022
EXTENSIONS
a(21)-a(39) from Alois P. Heinz, Sep 29 2022
STATUS
approved
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Last modified August 22 00:18 EDT 2024. Contains 375353 sequences. (Running on oeis4.)