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

Terms

a(0) =0a(1) =6a(2) =54a(3) =324a(4) =1620a(5) =7290a(6) =30618a(7) =122472a(8) =472392a(9) =1771470a(10) =6495390a(11) =23383404a(12) =82904796a(13) =290166786a(14) =1004423490a(15) =3443737680a(16) =11708708112a(17) =39516889878a(18) =132497807238a(19) =441659357460