11

This number is a prime.

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+ 11 is the (1+1)nd odd prime that cannot be expressed as the sum of two prime numbers. [Astle]

+ 11 is the smallest number of sides of a regular polygon that cannot be packed about a point with other regular polygons. E.g., a 7-sided polygon packs with a 42-sided polygon and a triangle. [Astle]

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