A288515 -id:A288515 - cp's OEIS frontend

A270919 Coefficient of x^n in Product_{k>=1} ((1 + x^k) / (1 - x^k))^n.

1, 2, 12, 80, 552, 3912, 28224, 206208, 1520784, 11297546, 84413912, 633713808, 4776117216, 36115518376, 273868321536, 2081866609920, 15859616674336, 121046064563376, 925411686479820, 7085465166635440, 54323193841192752, 416993869451825424, 3204447137019290944

Offset: 0

Vaclav Kotesovec, Mar 25 2016

nonn

From Peter Bala, Apr 18 2023: (Start)
The Gauss congruences a(n*p^k) == a(n*p^(k-1)) (mod p^k) hold for all primes p and all positive integers n and k.
Conjecture: the supercongruence a(p) == 2*p + 2 (mod p^2) holds for all primes p. Cf. A291697. (End)

Seiichi Manyama, Table of n, a(n) for n = 0..1118 (terms 0..500 from Vaclav Kotesovec)

Main diagonal of A288515.

Cf. A008485, A008705, A156616, A270913, A270923, A270924, A291697, A309986, A362408.

Table[SeriesCoefficient[Product[((1+x^k)/(1-x^k))^n, {k, 1, n}], {x, 0, n}], {n, 0, 25}]
Table[SeriesCoefficient[(QPochhammer[-1, x]/QPochhammer[x, x])^n, {x, 0, n}]/2^n, {n, 0, 25}]
(* Calculation of constants {d,c}: *) eq = FindRoot[{2*s*QPochhammer[r*s] == QPochhammer[-1, r*s], (Log[1 - r*s] + QPolyGamma[0, 1, r*s])/Log[r*s] + r*((Derivative[0, 1][QPochhammer][-1, r*s] - 2*s*Derivative[0, 1][QPochhammer][r*s, r*s]) / (2*QPochhammer[r*s])) == 1}, {r, 1/8}, {s, 2}, WorkingPrecision -> 1000]; {N[1/r /. eq, 120], val = Sqrt[(1 - r*s)*Log[r*s]^2*(QPochhammer[r*s] / (Pi*(-r*s*(-1 + r*s) * Log[r*s]*(4*(2*ArcTanh[1 - 2*r*s] + QPolyGamma[0, 1, r*s])* Derivative[0, 1][QPochhammer][r*s, r*s] + r*Log[r*s]*(Derivative[0, 2][QPochhammer][-1, r*s] - 2*s*Derivative[0, 2][QPochhammer][r*s, r*s])) + 2*QPochhammer[r*s] * (4*r*s*ArcTanh[1 - 2*r*s] + 2*(-1 + (-1 + r*s)*ArcTanh[1 - 2*r*s])*Log[1 - r*s] - (-1 + r*s)*(-2 + Log[r*s] - 2*Log[1 - r*s])*QPolyGamma[0, 1, r*s] + (-1 + r*s) * QPolyGamma[0, 1, r*s]^2 + (-1 + r*s)*(QPolyGamma[1, 1, r*s] - 2*r*s*Log[r*s]* Derivative[0, 0, 1][QPolyGamma][0, 1, r*s])))))] /. eq; N[Chop[val], -Floor[Log[10, Abs[Im[val]]]] - 3]} (* Vaclav Kotesovec, Oct 03 2023 *)

a(n) ~ c * d^n / sqrt(n), where d = 7.862983395705905261519347909953827161057584... and c = 0.299856802806668079413694689903953367699319...

a(n) = [x^n] 1/theta_4(x)^n, where theta_4() is the Jacobi theta function. - Ilya Gutkovskiy, Nov 03 2017

A299108 Expansion of 1/(1 - x*Product_{k>=1} (1 + x^k)/(1 - x^k)).

Original entry on oeis.org

1, 1, 3, 9, 27, 79, 231, 675, 1971, 5755, 16805, 49071, 143289, 418411, 1221781, 3567663, 10417761, 30420401, 88829145, 259385701, 757419669, 2211704625, 6458291945, 18858546645, 55067931981, 160801210705, 469547855419, 1371104033121, 4003694720243

Offset: 0

Ilya Gutkovskiy, Feb 02 2018

nonn

Vaclav Kotesovec, Table of n, a(n) for n = 0..2000
N. J. A. Sloane, Transforms

Antidiagonal sums of A288515.

Cf. A015128, A032803, A067687, A299105, A299106.

S:= series(1/(1-x/JacobiTheta4(0,x)),x,51):
seq(coeff(S,x,n),n=0..50); # Robert Israel, Feb 02 2018

nmax = 28; CoefficientList[Series[1/(1 - x Product[(1 + x^k)/(1 - x^k), {k, 1, nmax}]), {x, 0, nmax}], x]
nmax = 28; CoefficientList[Series[1/(1 - x/EllipticTheta[4, 0, x]), {x, 0, nmax}], x]
nmax = 28; CoefficientList[Series[1/(1 - x QPochhammer[-x, x]/QPochhammer[x, x]), {x, 0, nmax}], x]

G.f.: 1/(1 - x*Product_{k>=1} (1 + x^k)/(1 - x^k)).
G.f.: 1/(1 - x/theta_4(x)), where theta_4() is the Jacobi theta function.
a(0) = 1; a(n) = Sum_{k=1..n} A015128(k-1)*a(n-k).
a(n) ~ c * d^n, where d = 2.9200517419026569743994130834319365190407162724411912701937027582419975778... is the root of the equation EllipticTheta(4, 0, 1/d) * d = 1 and c = 0.372842695601022868809531452599286285949969156503576039087883242107... = 2*Log[r]*QPochhammer[r] / (2*QPochhammer[r] * (Log[1 - r] + Log[r] + QPolyGamma[1, r]) + r*Log[r] * (r * Derivative[0, 1][QPochhammer][-1, r] - 2*Derivative[0, 1][QPochhammer][r, r])), where r = 1/d. Equivalently, c = EllipticTheta[4, 0, r]^2 / (r *(EllipticTheta[4, 0, r] - r * Derivative[0, 0, 1][EllipticTheta][4, 0, r])). - Vaclav Kotesovec, Feb 03 2018, updated Mar 31 2018

A284286 Expansion of eta(q^2)^4 / eta(q)^8 in powers of q.

Original entry on oeis.org

1, 8, 40, 160, 552, 1712, 4896, 13120, 33320, 80872, 188784, 425952, 932640, 1988080, 4137024, 8422848, 16810536, 32943760, 63482760, 120440608, 225217904, 415498496, 756920160, 1362645440, 2425895712, 4273590392, 7454092720, 12879684160, 22056267840

Offset: 0

Seiichi Manyama, May 02 2017

nonn

Seiichi Manyama, Table of n, a(n) for n = 0..10000

Column k=4 of A288515.

Cf. A002131, A004405, A096727.

# JacobiTheta4 is defined in A002448.
A284286List(len) = JacobiTheta4(len, -4)
A284286List(29) |> println # Peter Luschny, Mar 12 2018

eta = QPochhammer;
CoefficientList[eta[q^2]^4/eta[q]^8 + O[q]^30, q] (* Jean-François Alcover, Feb 21 2021 *)

a(n) = (-1)^n * A004405(n).
a(0) = 1, a(n) = (8/n)*Sum_{k=1..n} A002131(k)*a(n-k) for n > 0.
G.f.: Prod_{k>0} (1 - x^(2k))^4 / (1 - x^k)^8.

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A270919 Coefficient of x^n in Product_{k>=1} ((1 + x^k) / (1 - x^k))^n.

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A299108 Expansion of 1/(1 - x*Product_{k>=1} (1 + x^k)/(1 - x^k)).

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A284286 Expansion of eta(q^2)^4 / eta(q)^8 in powers of q.

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