a(n) = numerator(b(n)), where b(0) = b(1) = 1 and b(n) = n*b(n-1)/b(n-2) for n >= 1.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =12a(5) =10a(6) =5a(7) =7a(8) =28a(9) =72a(10) =180a(11) =275a(12) =55a(13) =91a(14) =2548a(15) =252a(16) =3600a(17) =18700a(18) =187a(19) =1729a(20) =12103a(21) =5880a(22) =13200a(23) =473110a(24) =4301a(25) =247a(26) =786695a(27) =171990a(28) =16632a(29) =5488076