a(0) = 0. If n is odd, a(n) = a(n-1) * n, otherwise a(n) = a(n-1) + n.

Terms

a(0) =0a(1) =0a(2) =2a(3) =6a(4) =10a(5) =50a(6) =56a(7) =392a(8) =400a(9) =3600a(10) =3610a(11) =39710a(12) =39722a(13) =516386a(14) =516400a(15) =7746000a(16) =7746016a(17) =131682272a(18) =131682290a(19) =2501963510a(20) =2501963530a(21) =52541234130a(22) =52541234152