OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..26
FORMULA
a(n) ~ exp(11/12) * n^(n^2 - n/2 + 1) / (2*Pi)^((n-1)/2). - Vaclav Kotesovec, May 24 2020
EXAMPLE
a(0) = 1: () = the empty sequence.
a(1) = 2: (), 1.
a(2) = 19: (), 1, 2, 11, 12, 21, 22, 112, 121, 122, 211, 212, 221, 1122, 1212, 1221, 2112, 2121, 2211.
MAPLE
b:= proc(n, k, i) option remember; `if`(k=0, 1,
`if`(i<1, 0, add(b(n, k-j, i-1)/j!, j=0..min(k, n))))
end:
a:= n-> add(b(n, k, n)*k!, k=0..n^2):
seq(a(n), n=0..10);
MATHEMATICA
Table[Sum[k!*SeriesCoefficient[Sum[x^j/j!, {j, 0, n}]^n, {x, 0, k}], {k, 0, n^2}], {n, 0, 10}] (* Vaclav Kotesovec, May 24 2020 *)
PROG
(PARI) {a(n) = sum(i=0, n^2, i!*polcoef(sum(j=0, n, x^j/j!)^n, i))} \\ Seiichi Manyama, May 19 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jul 04 2016
STATUS
approved