3782742017domain: NAppears in sequencesDivisorial primes: Primes p such that p = 1 + Product_{d|n} d for some n (ordered by n).at n=18A118370Divisorial primes p such that p-1 = Product_{d|k} d for some k < sqrt(p-1).at n=7A258897Primes of the form: 1 + sigma(n)^4.at n=25A259310