135491domain: NAppears in sequencesNumbers k such that the period of the continued fraction for sqrt(k) contains exactly 57 ones.at n=18A031825a(n) = Sum_{1 <= x_1 <= x_2 <= x_3 <= x_4 <= n} gcd(x_1, x_2, x_3 , x_4, n).at n=39A343518