Triangular numbers congruent to 1 or 5 mod 6.

Terms

a(0) =1a(1) =55a(2) =91a(3) =253a(4) =325a(5) =595a(6) =703a(7) =1081a(8) =1225a(9) =1711a(10) =1891a(11) =2485a(12) =2701a(13) =3403a(14) =3655a(15) =4465a(16) =4753a(17) =5671a(18) =5995a(19) =7021a(20) =7381a(21) =8515a(22) =8911a(23) =10153a(24) =10585a(25) =11935a(26) =12403a(27) =13861a(28) =14365a(29) =15931