A122018 Modulo 2 recursion switch between A000898 and A121966: A000898 first.

1, 2, 6, 2, 40, 32, 464, 272, 7040, 4864, 136448, 87808, 3177472, 2123776, 86861824, 57128960, 2720112640, 1806049280, 96095928320, 63587041280, 3778819358720, 2507078533120, 163724570132480, 108568842403840, 7748467910901760

Offset: 0

Author

Roger L. Bagula, Sep 11 2006

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 0..731

Crossrefs

Cf. A000898, A121966.

Programs

Maple

f:= proc(n) option remember; if n::odd then procname(n-1)-(n-1)*procname(n-2) else 2*procname(n-1)+2*(n-1)*procname(n-2) fi end proc:
f(0):= 1: f(1):= 2:
map(f, [$0..50]); # Robert Israel, Jun 20 2018

Mathematica

a[0] = 1; a[1] = 2; a[n_] := a[n] = If[Mod[n, 2] == 1, a[n - 1] - (n - 1)*a[n - 2], 2*(a[n - 1] + (n - 1)*a[n - 2])] b = Table[a[n], {n, 0, 30}]

Formula

For n>=2, a(n) = a(n-1) - (n-1)*a(n-2) if n is odd, a(n) = 2*a(n-1) + 2*(n-1)*a(n-2) if n is even. - Edited by Robert Israel, Jun 20 2018

Extensions

Offset changed by Robert Israel, Jun 20 2018