345676543

This number is a prime.

Former editor Léo Sauvé once pointed out the particularly attractive nine-digit palindromic prime 345676543 in an issue of the problem solving journal Crux Mathematicorum.

If the digits of the prime, reading left to right, steadily increase to a maximum value, and then steadily decrease, they are called peak primes. Valley primes are just the opposite. There are a total of 10 peak and 20 valley primes. 345676543 is unique because of the five consecutive digits. [Heinz]