Generalized octagonal numbers: k*(3*k-2), k=0, +- 1, +- 2, +-3, ...

Terms

a(0) =0a(1) =1a(2) =5a(3) =8a(4) =16a(5) =21a(6) =33a(7) =40a(8) =56a(9) =65a(10) =85a(11) =96a(12) =120a(13) =133a(14) =161a(15) =176a(16) =208a(17) =225a(18) =261a(19) =280a(20) =320a(21) =341a(22) =385a(23) =408a(24) =456a(25) =481a(26) =533a(27) =560a(28) =616a(29) =645