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A007604
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a(n) = a(n-1) + a(n-1-(number of odd terms so far)).
(Formerly M0567)
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6
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1, 2, 3, 4, 6, 9, 12, 16, 22, 31, 40, 52, 68, 90, 121, 152, 192, 244, 312, 402, 523, 644, 796, 988, 1232, 1544, 1946, 2469, 2992, 3636, 4432, 5420, 6652, 8196, 10142, 12611, 15080, 18072, 21708, 26140, 31560, 38212, 46408, 56550, 69161, 81772, 96852
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OFFSET
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1,2
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COMMENTS
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A003056(n) gives the number of odd terms in the first n terms of this sequence. Modulo 2, this sequence becomes A023531. - T. D. Noe, Jul 24 2007
The present definition was the original definition of this sequence. It was later changed to "Sequence formed from rows of triangle A046936", but this seems less satisfactory. - N. J. A. Sloane, Oct 26 2014
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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MAPLE
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A[1]:= 1: A[2]:= 2: o:= 1:
for n from 3 to 100 do
A[n]:= A[n-1] + A[n-1-o];
if A[n]::odd then o:= o+1 fi
od:
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MATHEMATICA
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a[n_Integer] := a[n] = Block[{c, k}, c = 0; k = 1; While[k < n, If[ OddQ[ a[k] ], c++ ]; k++ ]; Return[a[n - 1] + a[n - 1 - c] ] ]; a[1] = 1; a[2] = 2; Table[ a[n], {n, 0, 60} ]
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PROG
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(Haskell)
a007604 n = a007604_list !! (n-1)
a007604_list = concat $ map tail $ tail a046936_tabl
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CROSSREFS
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KEYWORD
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nonn,nice,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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