a(n) = 441*n^2 - 21.

Terms

a(0) =420a(1) =1743a(2) =3948a(3) =7035a(4) =11004a(5) =15855a(6) =21588a(7) =28203a(8) =35700a(9) =44079a(10) =53340a(11) =63483a(12) =74508a(13) =86415a(14) =99204a(15) =112875a(16) =127428a(17) =142863a(18) =159180a(19) =176379a(20) =194460a(21) =213423a(22) =233268a(23) =253995a(24) =275604a(25) =298095a(26) =321468a(27) =345723a(28) =370860a(29) =396879