Indices k such that 19 plus the k-th triangular number is a perfect square.

Terms

a(0) =3a(1) =9a(2) =30a(3) =60a(4) =179a(5) =353a(6) =1046a(7) =2060a(8) =6099a(9) =12009a(10) =35550a(11) =69996a(12) =207203a(13) =407969a(14) =1207670a(15) =2377820a(16) =7038819a(17) =13858953a(18) =41025246a(19) =80775900a(20) =239112659a(21) =470796449a(22) =1393650710a(23) =2744002796a(24) =8122791603a(25) =15993220329a(26) =47343098910a(27) =93215319180a(28) =275935801859