641

This number is a prime.

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641 divides all the Generalized Fermat numbers of the form (2^a*5^b)^2^5 + 1, where a is odd and b is even, or a is even and b is odd. [Gallot]

Submitted: 1999-09-22 20:12:53;   Last Modified: 2008-01-30 11:28:00.
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