28442407domain: NAppears in sequencesa(n) is the least composite x such that sigma(x) divides (x-1)^n but not (x-1)^(n-1), for n >= 2.at n=23A254352Nonprime numbers k such that sum of the divisors of k is a power of 2.at n=33A254603Sphenic numbers that are the product of Mersenne primes.at n=12A346138