OFFSET
0,2
FORMULA
a(n) ~ 2^(n^2) / n!. - Vaclav Kotesovec, Oct 09 2020
EXAMPLE
a(2) = [x^2] (1+x)^4*(1+x^2)^2*(1+x^4) = 8;
a(3) = [x^3] (1+x)^8*(1+x^2)^4*(1+x^4)^2*(1+x^8) = 88;
a(4) = [x^4] (1+x)^16*(1+x^2)^8*(1+x^4)^4*(1+x^8)^2*(1+x^16) = 2812.
MATHEMATICA
Table[SeriesCoefficient[Product[(1 + x^(2^j))^(2^(n-j)), {j, 0, n}], {x, 0, n}], {n, 0, 15}] (* Vaclav Kotesovec, Oct 09 2020 *)
PROG
(PARI) {a(n)=polcoeff(prod(i=0, #binary(n), (1 + x^(2^i) +x*O(x^n))^(2^(n-i))), n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Aug 18 2007
STATUS
approved