This number is a prime.
683 = prime(6*8*3) - 6*8*3. Note that the prime 683 is the smallest number greater than one with this property. Note that the next such number is also prime. [Firoozbakht]
Regarding light, the maximum possible efficacy is 683 lumens per watt which corresponds to an efficiency of 100%. [Homewood]
The smallest prime whose the square consists of all the composite digits, i.e., 683^2=466489. [Loungrides]
There are 683 six-digit squares. [Gaydos]
Smallest Wagstaff prime p such that (2^p+1)/3 is not prime.