a(n) = 2^(n-4)*n*(n+1)*(n^2+5*n-2).

Terms

a(0) =0a(1) =1a(2) =18a(3) =132a(4) =680a(5) =2880a(6) =10752a(7) =36736a(8) =117504a(9) =357120a(10) =1041920a(11) =2939904a(12) =8067072a(13) =21618688a(14) =56770560a(15) =146472960a(16) =372113408a(17) =932511744a(18) =2308571136a(19) =5653135360a(20) =13707509760a(21) =32942063616a(22) =78525759488a(23) =185799278592a(24) =436627046400