1930499domain: NAppears in sequencesComposite squarefree numbers k such that k^2-1 is divisible by p-1 and p+1, where p are all the prime factors of k.at n=20A306685Composite squarefree numbers k such that for any prime p dividing k both (p-1)/2 and (p+1)/2 divide k+1.at n=3A392557