22427...41183 (47-digits)

This number is a prime.

                         2242745 2848394140 2769470443 9799166361 1794141183

The largest known prime factor in the 10th term of the Lucas-Lehmer sequence, i.e., (((((((((4^2-2)^2-2)^2-2)^2-2)^2-2)^2-2)^2-2)^2-2)^2-2)^2-2, as of December 15, 2010. [Mathar]