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

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =8a(6) =5a(7) =16a(8) =35a(9) =128a(10) =63a(11) =256a(12) =231a(13) =1024a(14) =429a(15) =2048a(16) =6435a(17) =32768a(18) =12155a(19) =65536a(20) =46189a(21) =262144a(22) =88179a(23) =524288a(24) =676039a(25) =4194304a(26) =1300075a(27) =8388608a(28) =5014575a(29) =33554432