OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..265
FORMULA
a(n) = n! * [x^n] exp(Sum_{j=1..n} (exp(j*x)-1)/j).
a(n) = A306024(n,n).
EXAMPLE
a(0) = 1: the empty string.
a(1) = 1: 1.
a(2) = 7: 11, 12, 13, 21, 22, 23, 24.
MAPLE
b:= proc(n, k, m) option remember; `if`(n=0, 1,
add(b(n-1, k, max(m, j)), j=1..m+k))
end:
a:= n-> b(n$2, 0):
seq(a(n), n=0..20);
# second Maple program:
a:= n-> n!*coeff(series(exp(add((exp(j*x)-1)/j, j=1..n)), x, n+1), x, n):
seq(a(n), n=0..20);
MATHEMATICA
b[n_, k_, m_] := b[n, k, m] = If[n == 0, 1,
Sum[b[n - 1, k, Max[m, j]], {j, 1, m + k}]];
a[n_] := b[n, n, 0];
Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Sep 07 2022, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jun 17 2018
STATUS
approved