13

This number is a prime.

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Photo credit: Patrick Kik
+ 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 is one curio for this number that has not yet been approved by an editor.)

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