a(n) = n*a(n-1) + n^(1+n mod 2), a(0) = 1.

Terms

a(0) =1a(1) =2a(2) =6a(3) =19a(4) =80a(5) =401a(6) =2412a(7) =16885a(8) =135088a(9) =1215793a(10) =12157940a(11) =133737341a(12) =1604848104a(13) =20863025353a(14) =292082354956