Ratios of successive terms are 1,1,2,3,3,4,5,5,6,7,7,...

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =18a(6) =72a(7) =360a(8) =1800a(9) =10800a(10) =75600a(11) =529200a(12) =4233600a(13) =38102400a(14) =342921600a(15) =3429216000a(16) =37721376000a(17) =414935136000