OFFSET
0,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..253
FORMULA
a(0) = 1 and a(n) = (n-1)! * Sum_{k=1..n} k*k!*a(n-k)/(n-k)! for n > 0.
a(n) ~ n!^2. - Vaclav Kotesovec, Oct 18 2017
MAPLE
a:= proc(n) option remember; `if`(n=0, 1, add(
a(n-i)*binomial(n-1, i-1)*i!^2, i=1..n))
end:
seq(a(n), n=0..20); # Alois P. Heinz, Dec 02 2021
MATHEMATICA
nmax = 20; CoefficientList[Series[E^Sum[k!*x^k, {k, 1, nmax}], {x, 0, nmax}], x] * Range[0, nmax]! (* Vaclav Kotesovec, Oct 18 2017 *)
PROG
(PARI) {a(n) = n!*polcoeff(exp(sum(k=1, n, k!*x^k)+x*O(x^n)), n)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Oct 17 2017
STATUS
approved