Fermat number

A Fermat number, named after Pierre de Fermat, is a number of the form:


 * $$F_{n} = 2^{2^{ \overset{n} {}}} + 1$$

It was originally conjectured that all Fermat numbers were prime, but this has been proven false; in fact, only the first five Fermat numbers (F0 to F4) are prime.

F333 is the first Fermat number that is larger than a googolplex,