OFFSET
0,3
LINKS
Eric Weisstein's World of Mathematics, Lambert W-Function.
FORMULA
E.g.f.: A(x) = exp( -LambertW(-x * (1+3*x)^(1/3)) ).
a(n) = n! * Sum_{k=0..n} (k+1)^(k-1) * 3^(n-k) * binomial(k/3,n-k)/k!.
a(n) ~ sqrt(4*r+1) * n^(n-1) / (exp(n - 5/2) * r^(n - 3/2)), where r = 0.29742497866288781360719311656731644994668261137281157848090655000... is the root of the equation r*(1 + 3*r)^(1/3) = exp(-1). - Vaclav Kotesovec, Apr 22 2024
PROG
(PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(exp(-lambertw(-x*(1+3*x)^(1/3)))))
(PARI) a(n) = n!*sum(k=0, n, (k+1)^(k-1)*3^(n-k)*binomial(k/3, n-k)/k!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 20 2024
STATUS
approved