Euler's totient function (nonfiction)
From Gnomon Chronicles
In number theory, Euler's totient function counts the positive integers up to a given integer n that are relatively prime to n
It is written using the Greek letter phi as φ and may also be called Euler's phi function.
In other words, it is the number of integers ... for which the greatest common divisor is equal to 1.
The integers ... of this form are sometimes referred to as totatives of ...
For example, the totatives of n = 9 are the six numbers 1, 2, 4, 5, 7 and 8. They are all relatively prime to 9, but the other three numbers in this range, 3, 6, and 9 are not, since ...
