Odd octagonal numbers indexed by triangular numbers.

Terms

a(0) =1a(1) =21a(2) =133a(3) =481a(4) =1281a(5) =2821a(6) =5461a(7) =9633a(8) =15841a(9) =24661a(10) =36741a(11) =52801a(12) =73633a(13) =100101a(14) =133141a(15) =173761a(16) =223041a(17) =282133a(18) =352261a(19) =434721a(20) =530881a(21) =642181a(22) =770133a(23) =916321a(24) =1082401a(25) =1270101a(26) =1481221a(27) =1717633a(28) =1981281a(29) =2274181