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

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =12a(5) =48a(6) =192a(7) =960a(8) =5760a(9) =34560a(10) =241920a(11) =1935360a(12) =15482880a(13) =139345920a(14) =1393459200a(15) =13934592000a(16) =153280512000