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A117586 Coefficients of q in series expansion of Zagier's identity. 0
0, -1, -2, -1, -1, 2, 0, 4, 1, 2, 1, 2, -4, 1, -1, -5, -2, -1, -3, -1, -2, -2, 5, 0, -1, 1, 8, 0, 3, 2, 2, 2, 3, 0, 4, -7, 0, 0, 2, -3, -8, -2, -1, -3, -2, -4, 0, -3, -3, -2, -1, 7, -1, 0, 1, -1, 0, 12, 2, 2, 0, 4, 3, 4, 0, 2, 4, 3, 0, 5, -12, 2, 0, 1, -1, 1, -3, -11, -1, -2, -6, 2, -4, -3, -3, -4, -2, 1, -5, -3, -3, -2, 11, 2, -2, -3, 2, 0, 0, 3, 12, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..101.

Robin Chapman, Franklin's argument proves an identity of Zagier, Electron. J. Combin. 7 #R54 (2000).

Eric Weisstein's World of Mathematics, Zagier's Identity

FORMULA

Negative of sequence is convolution of A010815 with A046746. - Michael Somos, Jan 07 2015

a(n) = A067661(n) - A067659(n) [Chapman]. - George Beck, May 06 2017

EXAMPLE

G.f. = - x - 2*x^2 - x^3 - x^4 + 2*x^5 + 4*x^7 + x^8 + 2*x^9 + x^10 + ...

MATHEMATICA

Flatten[{0, CoefficientList[Series[-Sum[x^(n - 1)*(QPochhammer[x^(n + 1), x]^2/QPochhammer[x^(n), x]), {n, 1, 101}], {x, 0, 100}], x]}] (* Mats Granvik, Jan 05 2015 *)

a[ n_] := SeriesCoefficient[ Sum[ QPochhammer[ x] - QPochhammer[ x, x, k], {k, 0, n}], {x, 0, n}]; (* Michael Somos, Jan 07 2015 *)

a[ n_] := SeriesCoefficient[ -Sum[ QPochhammer[ x^k, x] x^k / (1 - x^k)^2, {k, n}], {x, 0, n}]; (* Michael Somos, Jan 07 2015 *)

CROSSREFS

Cf. A046746.

Sequence in context: A123223 A088226 A244658 * A307988 A268917 A176811

Adjacent sequences:  A117583 A117584 A117585 * A117587 A117588 A117589

KEYWORD

sign

AUTHOR

Eric W. Weisstein, Mar 29 2006

STATUS

approved

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Last modified March 30 07:43 EDT 2020. Contains 333119 sequences. (Running on oeis4.)