with 1 excluded the smallest prime is therefore 2 however since 2 is the only even prime which ironically in some sense makes it the oddest prime it is also somewhat special and the set of all primes excluding 2 is therefore called the odd primesarge primes caldwell include the large mersenne primes ferrier s prime and the digit counterexample showing that 5359 is not a sierpiÅski number of the second kind helm and norris the largest known prime as of january 2013 is the mersenne prime which has a whopping decimal digits