a(n) = n^2 - 3.

Terms

a(0) =1a(1) =6a(2) =13a(3) =22a(4) =33a(5) =46a(6) =61a(7) =78a(8) =97a(9) =118a(10) =141a(11) =166a(12) =193a(13) =222a(14) =253a(15) =286a(16) =321a(17) =358a(18) =397a(19) =438a(20) =481a(21) =526a(22) =573a(23) =622a(24) =673a(25) =726a(26) =781a(27) =838a(28) =897a(29) =958