A232205 a(0)=1; thereafter a(n) = n*a(n-1) if n is even, otherwise a(n) = 2*n*a(n-1).
1, 2, 4, 24, 96, 960, 5760, 80640, 645120, 11612160, 116121600, 2554675200, 30656102400, 797058662400, 11158821273600, 334764638208000, 5356234211328000, 182111963185152000, 3278015337332736000, 124564582818643968000, 2491291656372879360000, 104634249567660933120000, 2301953490488540528640000
Offset: 0
Keywords
Programs
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Maple
c:=proc(n) option remember; if n=0 then 1 elif (n mod 2) = 0 then n*c(n-1) else 2*n*c(n-1); fi; end; [seq(c(n),n=0..20)];
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Mathematica
nxt[{n_,a_}]:={n+1,If[OddQ[n],a(n+1),2a(n+1)]}; NestList[nxt,{0,1},30][[All,2]] (* Harvey P. Dale, Jul 20 2020 *)
Formula
a(n) = n!*2^floor((n+1)/2). - Jon E. Schoenfield, Nov 24 2013
Extensions
Definition corrected to match terms by Jon E. Schoenfield, Nov 24 2013