This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A122018 #16 Jun 20 2018 07:17:35
%S A122018 1,2,6,2,40,32,464,272,7040,4864,136448,87808,3177472,2123776,
%T A122018 86861824,57128960,2720112640,1806049280,96095928320,63587041280,
%U A122018 3778819358720,2507078533120,163724570132480,108568842403840,7748467910901760
%N A122018 Modulo 2 recursion switch between A000898 and A121966: A000898 first.
%H A122018 Robert Israel, <a href="/A122018/b122018.txt">Table of n, a(n) for n = 0..731</a>
%F A122018 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
%p A122018 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:
%p A122018 f(0):= 1: f(1):= 2:
%p A122018 map(f, [$0..50]); # _Robert Israel_, Jun 20 2018
%t A122018 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}]
%Y A122018 Cf. A000898, A121966.
%K A122018 nonn
%O A122018 0,2
%A A122018 _Roger L. Bagula_, Sep 11 2006
%E A122018 Offset changed by _Robert Israel_, Jun 20 2018