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A115273
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a(n) = floor(n/3)*(n mod 3).
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10
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0, 0, 0, 0, 1, 2, 0, 2, 4, 0, 3, 6, 0, 4, 8, 0, 5, 10, 0, 6, 12, 0, 7, 14, 0, 8, 16, 0, 9, 18, 0, 10, 20, 0, 11, 22, 0, 12, 24, 0, 13, 26, 0, 14, 28, 0, 15, 30, 0, 16, 32, 0, 17, 34, 0, 18, 36, 0, 19, 38, 0, 20, 40, 0, 21, 42, 0, 22, 44, 0, 23, 46, 0, 24, 48, 0, 25, 50, 0, 26, 52, 0, 27, 54, 0, 28, 56
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OFFSET
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0,6
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COMMENTS
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Three arithmetic progressions interlaced: a(1)=1,2,0 and d=a(n+1)-a(n)=1,2,0. Cf. A115274(n) = n+a(n), n=1,2,3,...
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LINKS
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FORMULA
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a(3k+1) = k, a(3k+2) = 2k, a(3k+3) = 0, k=1, 2, ...
G.f.: x^4*(2*x+1) / ((x-1)^2*(x^2+x+1)^2). - Colin Barker, May 11 2015
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MATHEMATICA
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Table[Floor[n/3]*Mod[n, 3], {n, 0, 104}] \\ Extended to offset 0 by M. F. Hasler, May 11 2015
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PROG
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(PARI) a(n, b=3)=(n=divrem(n, b))[1]*n[2] \\ M. F. Hasler, May 10 2015
(Python)
from math import prod
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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a(0)-a(3) and cross-references added by M. F. Hasler, May 11 2015
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STATUS
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approved
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