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

Terms

a(0) =6a(1) =90a(2) =810a(3) =5508a(4) =31590a(5) =161838a(6) =765450a(7) =3411720a(8) =14526054a(9) =59639490a(10) =237731274a(11) =924707340a(12) =3523453830a(13) =13191428502a(14) =48642794730a(15) =177008116752a(16) =636661003590