OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..366
FORMULA
EXAMPLE
a(2) = 6: 1243, 1324, 1432, 2134, 3214, 4231.
MAPLE
a:= proc(n) option remember; `if`(n<2, 1-n,
(4*n-2)*((n-1)*a(n-1)+(4*n-6)*a(n-2))/n)
end:
seq(a(n), n=0..20);
MATHEMATICA
a[n_] := Binomial[2n, n] Subfactorial[n];
a /@ Range[0, 20] (* Jean-François Alcover, Sep 01 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Apr 12 2017
STATUS
approved