a(n) = 2^(n-4)*(5*binomial(n,5) + 6*binomial(n,4)).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =6a(5) =70a(6) =480a(7) =2520a(8) =11200a(9) =44352a(10) =161280a(11) =549120a(12) =1774080a(13) =5491200a(14) =16400384a(15) =47523840a(16) =134184960a(17) =370442240a(18) =1002700800a(19) =2667184128a(20) =6985482240a(21) =18042716160a(22) =46022000640a(23) =116064256000a(24) =289696382976a(25) =716282265600