1073758207domain: NAppears in sequencesNumbers k such that k*sigma(k)*sigma(sigma(k)) is a triangular number.at n=4A116005Primes of the form m = 4^i + 4^j - 1, where i > j >= 0.at n=35A239714Primes of the form q*2^h - 1, where q is a Fermat prime.at n=26A336116