This number is a composite.
68 is the smallest composite number that becomes prime when turned upside down. Has the world been turned upside down? [Honaker]
The largest even number that is expressible as the sum of two primes in two different ways: (7 + 61) and (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]
68 = π(7)*prime(7). Note that 7 is the mean average of the digits of 68. [Worrom]
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