OFFSET
0,2
FORMULA
a(n) ~ exp(Pi*sqrt(n)/2) / (2^(5/4) * n^(3/4)).
MATHEMATICA
nmax=50; CoefficientList[Series[Product[(1+x^(4*k+1))^3, {k, 0, nmax}], {x, 0, nmax}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Aug 27 2015
STATUS
approved