a(0) = 1; thereafter a(n) = denominator of (n-2)!! / (n-1)!!.

Terms

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