a(n) = 3*(3*n+1)*(9*n+8)/2.

Terms

a(0) =12a(1) =102a(2) =273a(3) =525a(4) =858a(5) =1272a(6) =1767a(7) =2343a(8) =3000a(9) =3738a(10) =4557a(11) =5457a(12) =6438a(13) =7500a(14) =8643a(15) =9867a(16) =11172a(17) =12558a(18) =14025a(19) =15573a(20) =17202a(21) =18912a(22) =20703a(23) =22575a(24) =24528a(25) =26562a(26) =28677a(27) =30873a(28) =33150a(29) =35508