Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #7 Feb 29 2024 10:47:34
%S 1,2,6,28,70,300,892,3544,9990,43340,127988,546120,1651356,7227896,
%T 22414008,99344944,312879302,1396285452,4486205892,20057934312,
%U 65293087284,292353604136,963327294536,4308913730256,14340603113372,64059675491512,215075154021384,958968160741328
%N a(n) = 2^n * [x^n] Product_{k>=1} ((1 + 2*x^k)/(1 - 2*x^k))^(1/4).
%F G.f.: Product_{k>=1} ((1 + 2*(2*x)^k)/(1 - 2*(2*x)^k))^(1/4).
%F a(n) ~ QPochhammer(-1, 1/2)^(1/4) * 4^n / (Gamma(1/4) * QPochhammer(1/2)^(1/4) * n^(3/4)).
%t nmax = 30; CoefficientList[Series[Product[(1 + 2*x^k)/(1 - 2*x^k), {k, 1, nmax}]^(1/4), {x, 0, nmax}], x] * 2^Range[0, nmax]
%t nmax = 30; CoefficientList[Series[Product[(1 + 2*(2*x)^k)/(1 - 2*(2*x)^k), {k, 1, nmax}]^(1/4), {x, 0, nmax}], x]
%Y Cf. A261584, A303346, A370750.
%Y Cf. A032302, A070933.
%Y Cf. A370736, A370732.
%K nonn
%O 0,2
%A _Vaclav Kotesovec_, Feb 29 2024