71

This number is a prime.

The largest of the supersingular primes, i.e., the set of primes that divide the order of the Monster group (an algebraic construction with 2^46 * 3^20 * 5^9 * 7^6 * 11^2 * 13^3 * 17 * 19 * 23 * 29 *31 * 41 * 47 * 59 * 71 elements).