56863...18433 (54-digits)

This number is a prime.

                 5686 3064753535 6955169033 4109408678 0483936074 2060818433

The largest known factor of the smallest Fermat number which has not been fully factorized as of March 2026 (F_12). Discovered in 2010 by Vang, Zimmerman and Krappe. [Reamy]