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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =6a(6) =18a(7) =54a(8) =216a(9) =1080a(10) =5400a(11) =27000a(12) =162000a(13) =1134000a(14) =7938000a(15) =55566000a(16) =444528000a(17) =4000752000a(18) =36006768000a(19) =324060912000