PrimeGrid has found the 13th Largest Known Prime!
 

13 938237*2^3752950-1 1129757 L521 2007 Woodall
[url]http://primes.utm.edu/primes/page.php?id=83407[/url]
This is the largest non Gimps non SB prime in the top 20 list.
At number 15 we find the 123 project, and at number 18 we find the PSP project. Numbers 18 and 19 are Generalized Fermat.

[B]Woodall Prime Search[/B]
Woodall Numbers are positive integers of the form Wn = n * 2^n - 1, where n is also a positive integer greater than zero. It is conjectured that there are infinitely many such primes. The Woodall numbers Wn are primes for n=2, 3, 6, 30, 75, 81, 115, 123, 249, 362, 384, 462, 512, 751, 822, 5312, 7755, 9531, 12379, 15822, 18885, 22971, 23005, 98726, 143018, 151023, 22971, ... 2013992, 2367906 and composite for all other n less than 2,367,906.

So this is W3752948 ie 3752948*2^3752948 -1