A264685 Expansion of Product_{k>=1} (1 + x^k)/(1 - 2*x^k).

1, 3, 9, 24, 60, 141, 324, 717, 1560, 3330, 7020, 14622, 30225, 61998, 126522, 257007, 520326, 1050396, 2116116, 4255584, 8547330, 17149350, 34382295, 68889840, 137969466, 276220962, 552865365, 1106356314, 2213644548, 4428657402, 8859340926, 17721640698

Offset: 0

Author

Vaclav Kotesovec, Nov 21 2015

Keywords

• nonn

Links

• Vaclav Kotesovec, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A000009, A006951, A070933, A261584, A264686.

Programs

Mathematica

nmax = 40; CoefficientList[Series[Product[(1 + x^k)/(1 - 2*x^k), {k, 1, nmax}], {x, 0, nmax}], x]

Formula

a(n) ~ c * 2^n, where c = A079555 / A048651 = Product_{k>=1} (2^k+1)/(2^k-1) = 8.25598793577825006554414084943227312652...