Numbers k such that the k-th triangular number contains only digits {1,2,5}.

Terms

a(0) =1a(1) =5a(2) =6a(3) =10a(4) =49a(5) =66a(6) =101a(7) =174a(8) =205a(9) =210a(10) =550a(11) =666a(12) =714a(13) =4806a(14) =5010a(15) =6498a(16) =6666a(17) =10114a(18) =14914a(19) =22410a(20) =66666a(21) =71449a(22) =471701a(23) =495005a(24) =666666a(25) =1500101a(26) =2246130a(27) =3241950a(28) =6666666a(29) =15591825