OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..449
FORMULA
a(n) = n! + n*(n-1)!! = n*((n-1)! + (n-1)!!).
MAPLE
a:= proc(n) option remember; `if`(n<5, [1, 2, 4, 12, 36]
[n+1], ((n-3)^2*n*a(n-1) +(n-4)*n*(n-1)*a(n-2)
-(n-3)*n*(n-1)*(n-2)*a(n-3))/((n-4)*(n-2)))
end:
seq(a(n), n=0..25); # Alois P. Heinz, Dec 07 2016
MATHEMATICA
Table[n! + n (n-1)!!, {n, 0, 20}] (* Bruno Berselli, Aug 11 2016 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Olivier Gérard, Aug 01 2016
STATUS
approved