a(1) = 1; a(n) = n!*(3/2) for n>=2.

Terms

a(0) =1a(1) =3a(2) =9a(3) =36a(4) =180a(5) =1080a(6) =7560a(7) =60480a(8) =544320a(9) =5443200a(10) =59875200a(11) =718502400a(12) =9340531200a(13) =130767436800