68

68 = 2² x 17.

68 is the smallest composite number that becomes prime when turned upside down: 89.

68 is the largest even number that is expressible as the sum of two primes in two different ways: 7 + 61 = 68 and 31 + 37 = 68.

68 has a representation as a sum of two squares: 68 = 2² + 8².

68 is 44 in base 16.


The chemical element erbium has atomic number 68.

Source: Prime Curios!