When learning algorithms, such as RSA, it is important to understand the mathematics being used. In RSA, the number of positive integers less than or equal to some number is critical in key generation. The number of positive integers less than or equal to n that are coprime to n is called ______.

Euler's totient https://en.wikipedia.org/wiki/Euler%27s_totient_function In number theory, Euler's totient function counts the positive integers up to a given integer n that are relatively prime to n. Incorrect answers: Fibonacci number - commonly denoted Fn, form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. Fermat's number - named after Pierre de Fermat, who first studied them, is a positive integer of the form Fn = 2^2^n+1 where n is a non-negative integer. The first few Fermat numbers are: 3, 5, 17, 257, 65537, 4294967297, 18446744073709551617, … Mersenne prime – prime number that is one less than a power of two. That is, it is a prime number of the form Mn = 2^n − 1 for some integer n. They are named after Marin Mersenne, a French Minim friar, who studied them in the early 17th century.