A320237 G.f.: Product_{k>=1, j>=1} ((1 + x^(k*j)) / (1 - x^(k*j)))^2.

1, 4, 16, 52, 156, 428, 1120, 2772, 6616, 15224, 34032, 74020, 157340, 327244, 667824, 1338828, 2641332, 5133372, 9840432, 18621476, 34818852, 64374564, 117768176, 213306948, 382733816, 680630120, 1200198784, 2099417544, 3644332860, 6280017740, 10746594208

Offset

0,2

Comments

Self-convolution of A301554.

Convolution of A320235 and A320236.

Links

Vaclav Kotesovec, Table of n, a(n) for n = 0..10000

Formula

Conjecture: log(a(n)) ~ Pi * sqrt(n*log(n)).

Mathematica

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

Crossrefs

Cf. A301554, A320235, A320236.

Sequence in context: A058234 A188125 A007688 * A197132 A266943 A100774

Adjacent sequences: A320234 A320235 A320236 * A320238 A320239 A320240

Keyword

nonn

Author

Vaclav Kotesovec, Oct 08 2018

Status

approved