https://en.wikipedia.org/wiki/Divisor
Further notions and facts. There are some elementary rules: If and , then , i.e. divisibility is a transitive relation.; If and , then = or =.; If and , then (+) holds, as does (). However, if and , then (+) does not always hold (e.g. and but 5 does not divide 6).; If , and (,) =, then . This is called Euclid's lemma.. If is a prime number and then or .. A positive divisor of which is ...