a(n) = 3*(n+1)*(9*n+4).

Terms

a(0) =12a(1) =78a(2) =198a(3) =372a(4) =600a(5) =882a(6) =1218a(7) =1608a(8) =2052a(9) =2550a(10) =3102a(11) =3708a(12) =4368a(13) =5082a(14) =5850a(15) =6672a(16) =7548a(17) =8478a(18) =9462a(19) =10500a(20) =11592a(21) =12738a(22) =13938a(23) =15192a(24) =16500a(25) =17862a(26) =19278a(27) =20748a(28) =22272a(29) =23850