Denominator of n!!/(n+3)!!.

Terms

a(0) =3a(1) =8a(2) =15a(3) =16a(4) =105a(5) =128a(6) =315a(7) =256a(8) =3465a(9) =1024a(10) =9009a(11) =2048a(12) =45045a(13) =32768a(14) =109395a(15) =65536a(16) =2078505a(17) =262144a(18) =4849845a(19) =524288a(20) =22309287a(21) =4194304a(22) =50702925a(23) =8388608a(24) =456326325a(25) =33554432a(26) =1017958725a(27) =67108864