OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..167
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
a(n) = Sum_{pi} n!/(k(1)! * 1!^k(1) * k(2)! * 2!^k(2) * ... * k(n)! * n!^k(n)) * (n!/(1!^k(1) * 2!^k(2) * ... * n!^k(n)))^L, where pi runs through all partitions k(1) + 2 * k( 2) + ... + n * k(n) = n, with L = 3.
a(0) = 1; a(n) = (1/n) * Sum_{k=0..n-1} binomial(n,k)^4 * (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!^3, i=1..n))
end:
a:= n-> b(n)*n!^3:
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!^3, {i, n}]];
a[n_] := b[n]*n!^3;
Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Mar 15 2017, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 18 2001
EXTENSIONS
Formula and more terms from Vladeta Jovovic, Dec 09 2001
STATUS
approved