81263domain: NAppears in sequencesNumbers k such that the least term in the periodic part of the continued fraction for sqrt(k) is 15.at n=20A031693Concatenations C1 and C2 and C3 and C4 are all prime (see the comment lines).at n=20A034819a(n) = 225n^2 + 2n.at n=18A158228