OFFSET
0,2
FORMULA
a(n) = n!*2^floor((n+1)/2). - Jon E. Schoenfield, Nov 24 2013
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)];
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 *)
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 21 2013
EXTENSIONS
Definition corrected to match terms by Jon E. Schoenfield, Nov 24 2013
STATUS
approved