65281

This number is a composite.

65281 is the smallest strong pseudoprime to base 16 with an even reciprocal period when written in hexadecimal. There is no other such number < 1.2*10^6. Note, we need only 4 different digits (0,1,e,f) to write this: 1/ff01 = 0.000100fffeff 000100fffeff... . [Yosei]