Octagonal numbers: n*(3*n-2). Also called star numbers.

Terms

a(0) =0a(1) =1a(2) =8a(3) =21a(4) =40a(5) =65a(6) =96a(7) =133a(8) =176a(9) =225a(10) =280a(11) =341a(12) =408a(13) =481a(14) =560a(15) =645a(16) =736a(17) =833a(18) =936a(19) =1045a(20) =1160a(21) =1281a(22) =1408a(23) =1541a(24) =1680a(25) =1825a(26) =1976a(27) =2133a(28) =2296a(29) =2465