OFFSET
0,4
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..450
FORMULA
a(n) ~ c * n!, where c = A247551/2 = 1.26473873603957632409005807712697712... - Vaclav Kotesovec, Sep 28 2019
MAPLE
b:= proc(n, i, k) option remember; `if`(n=0, 1,
`if`(i>n, 0, b(n, i+1, `if`(i=k, 0, k))+
`if`(i=k, 0, b(n-i, i, k)*binomial(n, i))))
end:
a:= n-> b(n, 1, 0)-b(n, 1, 2):
seq(a(n), n=0..23);
MATHEMATICA
b[n_, i_, k_] := b[n, i, k] = If[n == 0, 1, If[i > n, 0, b[n, i + 1, If[i == k, 0, k]] + If[i == k, 0, b[n - i, i, k] Binomial[n, i]]]];
a[n_] := b[n, 1, 0] - b[n, 1, 2];
a /@ Range[0, 23] (* Jean-François Alcover, Dec 18 2020, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 26 2019
STATUS
approved