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

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =24a(6) =96a(7) =384a(8) =1536a(9) =7680a(10) =46080a(11) =276480a(12) =1658880a(13) =11612160a(14) =92897280a(15) =743178240a(16) =5945425920a(17) =53508833280a(18) =535088332800