Odd triangular numbers.

Terms

a(0) =1a(1) =3a(2) =15a(3) =21a(4) =45a(5) =55a(6) =91a(7) =105a(8) =153a(9) =171a(10) =231a(11) =253a(12) =325a(13) =351a(14) =435a(15) =465a(16) =561a(17) =595a(18) =703a(19) =741a(20) =861a(21) =903a(22) =1035a(23) =1081a(24) =1225a(25) =1275a(26) =1431a(27) =1485a(28) =1653a(29) =1711