a(n) = n^2 - 4.

Terms

a(0) =0a(1) =5a(2) =12a(3) =21a(4) =32a(5) =45a(6) =60a(7) =77a(8) =96a(9) =117a(10) =140a(11) =165a(12) =192a(13) =221a(14) =252a(15) =285a(16) =320a(17) =357a(18) =396a(19) =437a(20) =480a(21) =525a(22) =572a(23) =621a(24) =672a(25) =725a(26) =780a(27) =837a(28) =896a(29) =957