400

This number is a composite.

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400 is the only known square of the form 1+p+p^2+p^3, where p is prime or composite. (Note that p=1 yields a square, but 1 is neither prime nor composite.) [Noe]

Submitted: 2009-03-16 11:09:35;   Last Modified: 2009-03-16 19:25:42.
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