a(n) = (2*n - 1) * a(n-2) for n>1, a(0) = a(1) = 1.

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =21a(5) =45a(6) =231a(7) =585a(8) =3465a(9) =9945a(10) =65835a(11) =208845a(12) =1514205a(13) =5221125a(14) =40883535a(15) =151412625a(16) =1267389585a(17) =4996616625a(18) =44358635475a(19) =184874815125