OFFSET
0,3
FORMULA
MAPLE
a := proc(n) option remember;
if n < 3 then return n fi;
if n mod 2 = 0 then return n*a(n-1) fi;
h := iquo(n, 2); n*a(n-1)/(h*(h+2)) end:
seq(a(n), n=0..36);
MATHEMATICA
t[n_, k_] /; (k > n || k < 0) = 0; t[n_, n_] = 1; t[n_, k_] := t[n, k] =
t[n - 1, k - 1] + Mod[n - k, 2] t[n - 1, k] + t[n - 1, k + 1];
a[n_] := t[n, 1];
Table[a[n], {n, 0, 36}] (* Jean-François Alcover, Jul 10 2019 *)
PROG
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Peter Luschny, Mar 01 2014
STATUS
approved