Euler's totient

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(n) or ϕ(n), and may also be called Euler's phi function. In other words, it is the number of integers k in the range 1 ≤ k ≤ n for which the greatest common divisor gcd(n, k) is equal to 1.[2][3] The integers k of this form are sometimes referred to as totatives of n. 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 gcd(9, 3) = gcd(9, 6) = 3 and gcd(9, 9) = 9. Therefore, φ(9) = 6. As another example, φ(1) = 1 since for n = 1 the only integer in the range from 1 to n is 1 itself, and gcd(1, 1) = 1.

function euler_totient(n)
{
  //Logic
  phi = new Array(n + 1).fill(1);
  phi[0] = 0;

  for(var i = 2; i <= n; i++)
  {
    phi[i] = i;
  }

  for(var i = 2; i <= n; i++)
  {
    if(phi[i] == i)
    {
      for(var j = i; j <= n; j += i)
      {
        phi[j] -= phi[j] / i;
      }
    }
  }
  return phi;
}