a(n) = 3*n^2.

Terms

a(0) =0a(1) =3a(2) =12a(3) =27a(4) =48a(5) =75a(6) =108a(7) =147a(8) =192a(9) =243a(10) =300a(11) =363a(12) =432a(13) =507a(14) =588a(15) =675a(16) =768a(17) =867a(18) =972a(19) =1083a(20) =1200a(21) =1323a(22) =1452a(23) =1587a(24) =1728a(25) =1875a(26) =2028a(27) =2187a(28) =2352a(29) =2523