OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..215
J.-M. Sixdeniers, K. A. Penson and A. I. Solomon, Extended Bell and Stirling Numbers From Hypergeometric Exponentiation, J. Integer Seqs. Vol. 4 (2001), #01.1.4.
FORMULA
G.f.: Sum_{n>=0} a(n)*x^n/n!^3 = exp( Sum_{n>=1} x^n/n!^3 ). [Paul D. Hanna, Mar 15 2012]
a(0) = 1; a(n) = (1/n) * Sum_{k=0..n-1} binomial(n,k)^3 * (n-k) * a(k). - Ilya Gutkovskiy, Jul 12 2020
MAPLE
b:= proc(n) option remember; `if`(n=0, 1,
add(b(n-i)*binomial(n-1, i-1)/i!^2, i=1..n))
end:
a:= n-> b(n)*n!^2:
seq(a(n), n=0..20); # Alois P. Heinz, May 11 2016
MATHEMATICA
b[n_] := b[n] = If[n==0, 1, Sum[b[n-i]*Binomial[n-1, i-1]/i!^2, {i, 1, n}]];
a[n_] := b[n]*n!^2;
Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Mar 14 2017, after Alois P. Heinz *)
PROG
(PARI) {a(n)=n!^3*polcoeff(exp(sum(m=1, n, x^m/m!^3)+x*O(x^n)), n)} /* Paul D. Hanna, Mar 15 2012 */
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 18 2001
EXTENSIONS
More terms from Karol A. Penson, Sep 10 2001
STATUS
approved