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

Terms

a(0) =6a(1) =108a(2) =972a(3) =6480a(4) =36450a(5) =183708a(6) =857304a(7) =3779136a(8) =15943230a(9) =64953900a(10) =257217444a(11) =994857552a(12) =3772168218a(13) =14061928860a(14) =51656065200a(15) =187339329792a(16) =671787127926