# 13

This number is a prime.

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There are 13 cubes that are each the concatentation of 2 five-digit prime numbers. [Gaydos]

m0000000000000n is composite for any two positive digits m and n. In fact, 13 zeros is the shortest string of zeros for which this is true. [Gaydos]

There are 13 squares with distinct digits that have the same sums of digits as their square roots. [Gaydos]

(There are 6 curios for this number that have not yet been approved by an editor.)

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