# Riesel number

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A **Riesel number** is a value of k such that k × 2^{n} - 1 is always composite.

Using the same method presented in the Sierpinski problem article, H.Riesel found in 1956 that 509203 × 2^{n} - 1 is always composite.

In order to demonstrate whether 509203 is the smallest Riesel number or not (the **Riesel problem**), a distributed computing project was created named Riesel Sieve.