Divisors and properties related to divisors are shown in table of divisors. Divisors of the form ("f") are also called principal divisors. Early applications include computing greatest common divisors of integers and polynomials. Sedgewick recommends to use gaps that have low greatest common divisors or are pairwise coprime. The series of reciprocals of all prime divisors of Fermat numbers is convergent. The sum of two effective Cartier divisors corresponds to multiplication of ideal sheaves. The Euclidean algorithm for computing greatest common divisors works by a sequence of Euclidean divisions. Hence those divisors form a Boolean algebra. A prime number is a positive integer which has exactly two divisors&colon; 1 and itself. First note that all the divisors of 20 are denominators. A positive integer that has no perfect square divisors except 1 is called square-free. An integer with exactly two positive divisors&colon; itself and 1. The elliptic curve method is a fast method for finding small prime divisors of numbers. The sum of proper divisors gives various other kinds of numbers. The group of all Weil divisors is denoted .