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A062105
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Square array read by antidiagonals: number of ways a pawn-like piece (with the initial 2-step move forbidden and starting from any square on the back rank) can end at various squares on an infinite chessboard.
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4
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1, 1, 2, 1, 3, 5, 1, 3, 8, 13, 1, 3, 9, 22, 35, 1, 3, 9, 26, 61, 96, 1, 3, 9, 27, 75, 171, 267, 1, 3, 9, 27, 80, 216, 483, 750, 1, 3, 9, 27, 81, 236, 623, 1373, 2123, 1, 3, 9, 27, 81, 242, 694, 1800, 3923, 6046, 1, 3, 9, 27, 81, 243, 721, 2038, 5211, 11257, 17303, 1, 3, 9, 27
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OFFSET
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0,3
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COMMENTS
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Table formatted as a square array shows the top-left corner of the infinite board.
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LINKS
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EXAMPLE
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Array begins:
1 1 1 1 1 1 1 1 1 1 1
2 3 3 3 3 3 3 3 3 3 3
5 8 9 9 9 9 9 9 9 9 ...
13 22 26 27 27 27 27 27 27 ...
35 61 75 80 81 81 81 ...
96 171 216 236 242 243 ...
267 483 623 694 721 ...
750 1373 1800 2038 ...
2123 3923 5211 ...
6046 11257 ...
17303 ...
...
Formatted as a triangle:
1,
1, 2,
1, 3, 5,
1, 3, 8, 13,
1, 3, 9, 22, 35,
1, 3, 9, 26, 61, 96,
1, 3, 9, 27, 75, 171, 267,
1, 3, 9, 27, 80, 216, 483, 750,
1, 3, 9, 27, 81, 236, 623, 1373, 2123,
1, 3, 9, 27, 81, 242, 694, 1800, 3923, 6046,
1, 3, 9, 27, 81, 243, 721, 2038, 5211, 11257, 17303,
...
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MAPLE
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[seq(CPTVSeq(j), j=0..91)]; CPTVSeq := n -> ChessPawnTriangleV( (2+(n-((trinv(n)*(trinv(n)-1))/2))), ((((trinv(n)-1)*(((1/2)*trinv(n))+1))-n)+1) );
ChessPawnTriangleV := proc(r, c) option remember; if(r < 2) then RETURN(0); fi; if(c < 1) then RETURN(0); fi; if(2 = r) then RETURN(1); fi; RETURN(ChessPawnTriangleV(r-1, c-1)+ChessPawnTriangleV(r-1, c)+ChessPawnTriangleV(r-1, c+1)); end;
M:=12; T:=Array(0..M, 0..M, 0);
T[0, 0]:=1; T[1, 1]:=1;
for i from 1 to M do T[i, 0]:=0; od:
for n from 2 to M do for k from 1 to n do
T[n, k]:= T[n, k-1]+T[n-1, k-1]+T[n-2, k-1];
od: od;
rh:=n->[seq(T[n, k], k=0..n)];
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MATHEMATICA
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T[n_, k_] := T[n, k] = If[n < 1 || k < 1, 0, If[n == 1, 1, T[n - 1, k - 1] + T[n - 1, k] + T[n - 1, k + 1]]]; Table[T[n - k + 1, k], {n, 1, 12}, {k, n, 1, -1}] // Flatten (* Jean-François Alcover, Mar 04 2016, adapted from PARI *)
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PROG
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(PARI) T(n, k)=if(n<1 || k<1, 0, if(n==1, 1, T(n-1, k-1)+T(n-1, k)+T(n-1, k+1)))
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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