262911domain: NAppears in sequencesNumbers k such that k and k^2 use only the digits 1, 2, 3, 6 and 9.at n=40A136981a(n) = pg(3, n) + pg(4, n) + ... + pg(n, n) where pg(m, n) is the n-th m-th-order polygonal number.at n=33A241452a(n) = Sum_{d|n} (n/d)^(n-n/d) * binomial(d+n-2,n-1).at n=9A363667