a(n) = numerator(n!! / (n - 1)!!).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =8a(5) =15a(6) =16a(7) =35a(8) =128a(9) =315a(10) =256a(11) =693a(12) =1024a(13) =3003a(14) =2048a(15) =6435a(16) =32768a(17) =109395a(18) =65536a(19) =230945a(20) =262144a(21) =969969a(22) =524288a(23) =2028117a(24) =4194304a(25) =16900975a(26) =8388608a(27) =35102025a(28) =33554432a(29) =145422675