OFFSET
0,2
FORMULA
G.f.: Product_{k>=1} 1/(1 - 3*(4*x)^k)^(1/2).
a(n) ~ 12^n / sqrt(Pi*QPochhammer(1/3)*n).
MATHEMATICA
nmax = 25; CoefficientList[Series[Product[1/(1-3*x^k), {k, 1, nmax}]^(1/2), {x, 0, nmax}], x] * 4^Range[0, nmax]
nmax = 25; CoefficientList[Series[Product[1/(1-3*(4*x)^k), {k, 1, nmax}]^(1/2), {x, 0, nmax}], x]
nmax = 25; CoefficientList[Series[Sqrt[-2/QPochhammer[3, x]], {x, 0, nmax}], x] * 4^Range[0, nmax]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Feb 27 2024
STATUS
approved