8951

This number is a prime.

The prime 8951 is the number of ways to choose 20 arithmetic operators (call them c1, c2, ..., c20) each either a * or / sign, so that 1 c1 2 c2 3 c3, ..., c20 21 is an integer. This is the largest known prime of that form. Curiously, it is also a prime that is a sum of twin primes and their indices, and a primitive prime divisor of (3^32-1)/2. [Post]