23

This number is a prime.

Let c = 2^a * 3^b with a,b>0 and prime p with p^n, n>1, c-p^k=prime. Is prime=23 the most common? E.g., 48-25=23, 72-49=23, 144-121=23, 192-169=23, 648-625=23, etc. [Bergot]