( 2^3021376 ) x ( 2^3021377 - 1 )

The largest known perfect number is

 (2^3021376)(2^3021377-1)

This number has 1,189,050 digits.

(A perfect number is a number that is equal to the sum of its proper factors.  For example, the proper factors of 28 are 1, 2, 4, 7, 14 and 1+2+4+7+14=28.)