OFFSET
0,3
FORMULA
E.g.f.: A(x) = Product_{k>=1} B(x^k), where B(x) = e.g.f. of Fubini numbers (A000670).
E.g.f.: Product_{j>=1} 1 / (1 - Sum_{i>=1} x^(i*j) / i!).
E.g.f.: exp(Sum_{k>=1} Sum_{d|k} (exp(x^(k/d)) - 1)^d / d).
a(n) ~ n! * c / (2 * (log(2))^(n+1)), where c = Product_{k>=2} (1/(2 - exp(log(2)^k)) = 10.38787833857244631... - Vaclav Kotesovec, Dec 11 2019
MATHEMATICA
nmax = 20; CoefficientList[Series[Product[1/(2 - Exp[x^k]), {k, 1, nmax}], {x, 0, nmax}], x] Range[0, nmax]!
nmax = 20; CoefficientList[Series[Exp[Sum[Sum[(Exp[x^(k/d)] - 1)^d/d, {d, Divisors[k]}], {k, 1, nmax}]], {x, 0, nmax}], x] Range[0, nmax]!
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 05 2019
STATUS
approved