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

Terms

a(0) =0a(1) =36a(2) =486a(3) =3888a(4) =24300a(5) =131220a(6) =642978a(7) =2939328a(8) =12754584a(9) =53144100a(10) =214347870a(11) =841802544a(12) =3233287044a(13) =12187005012a(14) =45199057050a(15) =165299408640a(16) =597144113712