Odd octagonal numbers: (2n+1)*(6n+1).

Terms

a(0) =1a(1) =21a(2) =65a(3) =133a(4) =225a(5) =341a(6) =481a(7) =645a(8) =833a(9) =1045a(10) =1281a(11) =1541a(12) =1825a(13) =2133a(14) =2465a(15) =2821a(16) =3201a(17) =3605a(18) =4033a(19) =4485a(20) =4961a(21) =5461a(22) =5985a(23) =6533a(24) =7105a(25) =7701a(26) =8321a(27) =8965a(28) =9633a(29) =10325