a(n) = n*3^n - n*2^n - n*1^n.

Terms

a(0) =0a(1) =0a(2) =8a(3) =54a(4) =256a(5) =1050a(6) =3984a(7) =14406a(8) =50432a(9) =172530a(10) =580240a(11) =1926078a(12) =6328128a(13) =20619690a(14) =66732176a(15) =214742070a(16) =687698944a(17) =2193154530a(18) =6968850192a(19) =22073006382a(20) =69714716480a(21) =219623377050a(22) =690291036688