second largest known Proth prime is , found by PrimeGrid. Proof The proof for this theorem uses the Pocklington-Lehmer primality test, and closely resembles the proof of Pépin's test. The proof can be found on page 52 of the book by Ribenboim in the references. History François Proth (1852–1879) published the theorem in 1878. See also Pépin's test (the special case k = 1, where one chooses a = 3) Sierpinski number References External links Primality tests Theorems about prime numbers de:Prothsche Primzahl nl:Prothgetal