Numbers k such that the k-th triangular number contains only digits {0,5,9}.

Terms

a(0) =10a(1) =34a(2) =44a(3) =100a(4) =109a(5) =1000a(6) =10000a(7) =10090a(8) =10099a(9) =31780a(10) =100000a(11) =1000000a(12) =1000999a(13) =1382685a(14) =4255724a(15) =10000000a(16) =10862780a(17) =13827219a(18) =100000000a(19) =100009900a(20) =100009909a(21) =100009955a(22) =100009999a(23) =100901000a(24) =1000000000a(25) =10000000000