178551domain: NAppears in sequencesNumbers k such that the period of the continued fraction for sqrt(k) contains exactly 71 ones.at n=21A031839Indices k such that s_k(4) is a (probable) prime, where s_k(4) = 4*s_{k-1}(4) - s_{k-2}(4), k >= 2, s_0(4) = 1, s_1(4) = 5.at n=29A299100