Euler's Totient Function

Problem

Given a number N, calculate the count of numbers in {1, 2, 3,…, N} that are relatively prime to N.

Solution

Euler’s Totient Function

• Gives the number of coprime numbers less tha a given number.

Algorithm is as follows-

• Initialize result as N
• For every number from 2 to phi(N)[Totient Function Value], divide N until it indivisible by it ans remove those numbers from result i.e.(result-=result/p).
• If reduced N is >1, remove all the multiples of N from the result too.

Reference - geeksforgeeks