# 2521

This number is a prime.

(2 * 2521) - 1 = 71^{2} and 2 * (2521 - 1) = 7!. [Forslund]

2521 minus one is the smallest EPRN.

2521^{2} = 1456^{3} - 1455^{3}, i.e., one solution to the Diophantine equation z^{2} = x^{3} - y^{3}. A Diophantine equation is a polynomial equation in which only integer solutions are allowed. These are named after the Greek algebraist Diophantus who lived in the 3rd century. [Mizuki]

The smallest prime formed by concatenating consecutive composite odd numbers. [Green]

The smallest prime that can be represented as the product of a number n and its reversal plus 1, in two ways, (n=120 and n=210). [Loungrides]

The smallest prime *p* such that *p* ≡ 1 mod
*d* , where *d* stands for any of the digits 2
through 9. [Beedassy]