159991977600domain: NAppears in sequencesNumbers k such that there is a proper divisor d of k satisfying sigma(d)=k.at n=21A081756Numbers k such that denominator(sigma(k)/k) = 6.at n=9A262359Sum of divisors of the multiply-perfect numbers.at n=20A307741Numbers k that have a record number of common divisors with sigma(k).at n=24A378267