En matemáticas, dos números enteros a y b son números primos entre sí (o coprimos, o primos relativos), si no tienen ningún factor primo en común, o, dicho de otra manera, si no tienen otro divisor común más que 1 y -1. Equivalentemente son primos entre sí, si y sólo si, su máximo común divisor es igual a 1. Por ejemplo, 6 y 35 son primos entre sí, pero 6 y 27 no lo son porque ambos son divisibles por 3. El 1 es primo respecto de todos los enteros, mientras que 0 sólo lo es respecto de 1 y -1. Un medio rápido para determinar si dos números enteros son primos entre sí es el algoritmo de Euclides.

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In number theory, two integers a and b are said to be relatively prime, mutually prime, or coprime (also spelled co-prime) if the only positive integer that divides both of them is 1. That is, the only common positive factor of the two numbers is 1. This is equivalent to their greatest common divisor being 1. The numerator and denominator of a reduced fraction are coprime. In addition to and the notation is sometimes used to indicate that a and b are relatively prime. For example, 14 and 15 are coprime, being commonly divisible by only 1, but 14 and 21 are not, because they are both divisible by 7. The numbers 1 and −1 are the only integers coprime to every integer, and they are the only integers to be coprime with 0. A fast way to determine whether two numbers are coprime is given by the Euclidean algorithm. The number of integers coprime to a positive integer n, between 1 and n, is given by Euler's totient function (or Euler's phi function) φ(n). A set of integers can also be called coprime if its elements share no common positive factor except 1. A set of integers is said to be pairwise coprime if a and b are coprime for every pair (a, b) of different integers in it.

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