68

This number is a composite.

+ 68 is the smallest composite number that becomes prime by turning it upside down. [Honaker]

+ The largest even number that is expressible as the sum of two primes in two different ways (7 + 61, 31 + 37). [Rivera]

+ 68 = -53+19+43+59. If -53 is considered to be a prime, then the sum of any three of these 4 primes is the square of a prime number; specifically the squares of the first 4 odd primes. [Rupinski]

(There are 3 curios for this number that have not yet been approved by an editor.)

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