a(n) = 2 * 3^(n-2)*n*(1+2*n).

Terms

a(0) =0a(1) =2a(2) =20a(3) =126a(4) =648a(5) =2970a(6) =12636a(7) =51030a(8) =198288a(9) =747954a(10) =2755620a(11) =9959598a(12) =35429400a(13) =124357194a(14) =431530092a(15) =1482720390a(16) =5050815264a(17) =17075199330a(18) =57338232372a(19) =191385721566a(20) =635369601960