Numbers k such that the k-th triangular number contains only digits {1,6,7}.

Terms

a(0) =1a(1) =3a(2) =11a(3) =18a(4) =36a(5) =48a(6) =58a(7) =188a(8) =351a(9) =366a(10) =576a(11) =1111a(12) =3941a(13) =11106a(14) =12423a(15) =17981a(16) =18263a(17) =34976a(18) =365423a(19) =392711a(20) =585963a(21) =1111411a(22) =1494106a(23) =568817576a(24) =1494099506a(25) =3651623506a(26) =12382820048a(27) =351330663666a(28) =586117934576