a(n) = 3*(9*n - 1)*(3*n - 2).

Terms

a(0) =6a(1) =24a(2) =204a(3) =546a(4) =1050a(5) =1716a(6) =2544a(7) =3534a(8) =4686a(9) =6000a(10) =7476a(11) =9114a(12) =10914a(13) =12876a(14) =15000a(15) =17286a(16) =19734a(17) =22344a(18) =25116a(19) =28050a(20) =31146a(21) =34404a(22) =37824a(23) =41406a(24) =45150a(25) =49056a(26) =53124a(27) =57354a(28) =61746a(29) =66300