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A110153
Expansion of g.f.: Product_{n>=1} 1/(1 - 3^n*x^n)^(3/3^n).
4
1, 3, 12, 39, 138, 426, 1461, 4458, 14655, 45309, 145479, 443037, 1427196, 4329696, 13655325, 41795679, 131102229, 397649811, 1247247507, 3775785681, 11761535064, 35770717695, 110693177805, 335003030301, 1040296817955, 3145674794979, 9695067728493, 29405519846121
OFFSET
0,2
EXAMPLE
A(x) = 1 + 3*x + 12*x^2 + 39*x^3 + 138*x^4 + 426*x^5 + ... =
1/[(1-3*x)*(1-9*x^2)^(1/3)*(1-27*x^3)^(1/9)*(1-81*x^4)^(1/27)*...].
MATHEMATICA
nmax=27; CoefficientList[Series[Product[1/(1 - 3^n*x^n)^(3/3^n), {n, nmax}], {x, 0, nmax}], x] (* Stefano Spezia, Jun 21 2024 *)
PROG
(PARI) a(n)=polcoeff(prod(k=1, n, 1/(1-3^k*x^k+x*O(x^n))^(3/3^k)), n)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jul 14 2005
EXTENSIONS
a(25)-a(27) from Stefano Spezia, Jun 21 2024
STATUS
approved