OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..224
Wikipedia, Permutation
MAPLE
b:= proc(n, k) b(n, k):= `if`(k=0, n!, b(n+1, k-1) -b(n, k-1)) end:
a:= n-> (2*n)! -b(0, 2*n):
seq(a(n), n=0..16);
MATHEMATICA
b[n_, k_] := b[n, k] = If[k == 0, n!, b[n + 1, k - 1] - b[n, k - 1]];
a[n_] := (2n)! - b[0, 2n];
a /@ Range[0, 16] (* Jean-François Alcover, Apr 02 2021, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Mar 04 2019
STATUS
approved