64995840domain: NAppears in sequencesNumbers k such that gcd(sigma(k),k) = k/5.at n=23A067237Numbers k for which sigma(k)/k - 2/5 is an integer.at n=7A218407Numbers k such that k divides lcm(tau(k), sigma(k)).at n=31A307740Abundant numbers k such that k^2 + A033880(k)^2 is a perfect square.at n=27A377134