683

683 is a prime number. It is a Sophie Germain prime because 2 x 683 + 1 is also a prime number.

683 is also a Wagstaff prime because it has the form (2^q + 1)/3, where q is another prime, 11.

683 is a divisor of 4¹¹ - 1.

683 is 838 in base 9.

The submarine USS Parche (SSN-683) was named for a small, coral-reef butterflyfish.

Source: What's Special About This Number?