311063879024domain: NAppears in sequencesNumbers k such that k' = sigma(k), where k' is the arithmetic derivative of k.at n=5A230164Numbers n such that Sum_{i=1..j} 1/d(i) - Sum_{i=1..k} 1/p(i) is an integer, where p are the prime factors of n, counted with multiplicity, and d its divisors.at n=22A238922