206197domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 100.at n=4A031688a(n) = Sum_{d|n} C(n,d)*sigma(d).at n=15A179305Prime numbersat n=18482