a(n) = n*3^n.

Terms

a(0) =0a(1) =3a(2) =18a(3) =81a(4) =324a(5) =1215a(6) =4374a(7) =15309a(8) =52488a(9) =177147a(10) =590490a(11) =1948617a(12) =6377292a(13) =20726199a(14) =66961566a(15) =215233605a(16) =688747536a(17) =2195382771a(18) =6973568802a(19) =22082967873a(20) =69735688020a(21) =219667417263a(22) =690383311398