Totient

The totient, specifically Euler's totient function, counts how many positive whole numbers up to a given number are relatively prime to it—that is, they share no common divisors other than 1. For example, for the number 10, the totient counts numbers like 1, 3, 7, and 9, which have no common factors with 10 (except 1). This concept helps in number theory, especially in understanding the properties of numbers and in cryptography, by measuring the "coprimality" within a range of integers.