TITLE: What is an odd prime?
QUESTION [49 upvotes]: I heard the term "odd prime" often. Isn't it redundant? If $n$ is even then $2$ divides $n$ so it's not prime. Why is "odd" emphasized?

REPLY [2 votes]: Think of a Venn diagram consisting of two intersecting circles, one labeled ODD NUMBERS, the other labeled PRIMES.  The number 1 is odd but not prime. The number 2 is prime but not odd. The intersection of the circles represents ODD PRIMES: 3, 5, 7,....