Indices k such that 25 plus the k-th triangular number is a perfect square.

Terms

a(0) =0a(1) =18a(2) =21a(3) =111a(4) =128a(5) =650a(6) =749a(7) =3791a(8) =4368a(9) =22098a(10) =25461a(11) =128799a(12) =148400a(13) =750698a(14) =864941a(15) =4375391a(16) =5041248a(17) =25501650a(18) =29382549a(19) =148634511a(20) =171254048a(21) =866305418a(22) =998141741a(23) =5049197999a(24) =5817596400a(25) =29428882578a(26) =33907436661a(27) =171524097471a(28) =197627023568