a(n) = T(2n,n-2), T given by A027157.

Terms

a(0) =5a(1) =21a(2) =176a(3) =680a(4) =5808a(5) =21840a(6) =190976a(7) =708480a(8) =6310400a(9) =23220736a(10) =209756160a(11) =767676416a(12) =7010676736a(13) =25558732800a(14) =235443322880a(15) =855858053120