Wilson prime

A Wilson prime is a special kind of prime number. A prime number p is a Wilson prime if (and only if [ [math]\displaystyle{ \iff }[/math] ])

[math]\displaystyle{ \frac{(p-1)!+1}{p^2}=n }[/math]

where n is a positive integer (sometimes called natural number). Wilson primes were first described by Emma Lehmer.[1]

The only known Wilson primes are 5, 13, and 563 (sequence A007540 in OEIS); if any others exist, they must be greater than 5×108.[2] It has been conjectured[3] that there are an infinite number of Wilson primes, and that the number of Wilson primes in an interval [math]\displaystyle{ [x,y] }[/math] is about

[math]\displaystyle{ \frac{\log \left ( \log y \right )}{\log x} }[/math].

Compare this with Wilson's theorem, which states that every prime p divides (p − 1)! + 1.

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