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

Terms

a(0) =0a(1) =3a(2) =36a(3) =243a(4) =1296a(5) =6075a(6) =26244a(7) =107163a(8) =419904a(9) =1594323a(10) =5904900a(11) =21434787a(12) =76527504a(13) =269440587a(14) =937461924a(15) =3228504075a(16) =11019960576a(17) =37321507107a(18) =125524238436a(19) =419576389587