Indices k such that 15 plus the k-th triangular number is a perfect square.

Terms

a(0) =1a(1) =4a(2) =6a(3) =11a(4) =20a(5) =33a(6) =43a(7) =70a(8) =121a(9) =196a(10) =254a(11) =411a(12) =708a(13) =1145a(14) =1483a(15) =2398a(16) =4129a(17) =6676a(18) =8646a(19) =13979a(20) =24068a(21) =38913a(22) =50395a(23) =81478a(24) =140281a(25) =226804a(26) =293726a(27) =474891a(28) =817620a(29) =1321913