13333331domain: NAppears in sequencesNumbers k such that the k-th triangular number contains only digits {4,6,8}.at n=11A119213Numbers k such that k and k^2 use only the digits 1, 3, 5, 6 and 7.at n=34A137033a(n) = n 3's sandwiched between two 1's.at n=6A185127