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

0,2

Links

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

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

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}]

Crossrefs

Cf. A000898, A121966.

Sequence in context: A345284 A200563 A284577 * A363395 A005729 A271504

Adjacent sequences: A122015 A122016 A122017 * A122019 A122020 A122021

Keyword

nonn

Author

Roger L. Bagula, Sep 11 2006

Extensions

Offset changed by Robert Israel, Jun 20 2018

Status

approved