a(n) = n*(n+2) = (n+1)^2 - 1.

Terms

a(0) =0a(1) =3a(2) =8a(3) =15a(4) =24a(5) =35a(6) =48a(7) =63a(8) =80a(9) =99a(10) =120a(11) =143a(12) =168a(13) =195a(14) =224a(15) =255a(16) =288a(17) =323a(18) =360a(19) =399a(20) =440a(21) =483a(22) =528a(23) =575a(24) =624a(25) =675a(26) =728a(27) =783a(28) =840a(29) =899