20707

This number is a prime.

The smaller term in the only known case of a pair of primes (20707, 59561) of form (p^m + q^n, p^n + q^m), where p, q are consecutive primes and m, n consecutive composite numbers, i.e., (2^10 + 3^9, 2^9 + 3^10). [Loungrides]