Numbers k such that the k-th triangular number contains only digits {1,2,6}.

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =36a(5) =66a(6) =111a(7) =651a(8) =666a(9) =1563a(10) =1588a(11) =5766a(12) =6651a(13) =6666a(14) =15563a(15) =15888a(16) =36366a(17) =65766a(18) =66651a(19) =66666a(20) =205748a(21) =363666a(22) =576406a(23) =657666a(24) =666651a(25) =666666a(26) =6657666a(27) =6666651a(28) =6666666a(29) =18014806