17672...80011 (73-digits)

This number is a prime.

                                                                         176
7251507175 7424308968 9188344017 7537264455 5816120481 6819161117 6760780011

The only known prime number of the form 3^x+5^x+17^x+257^x+65537^x. Note that bases are the all known Fermat primes. [Sariyar]