mathball/lib/totient/index.js

A JavaScript library for Competitive Programming

'use strict';

/* count of numbers having gcd 1 till num
 * Function: phi()
 */

var validate = require('../validation/non-negative-integer');

function phi(num) {
  var result = num;

  for (var i = 3; i <= Math.sqrt(num); i = i + 1) {
    if (num % i == 0) {
      while (num % i == 0) {
        num = num / i;
      }
      result = result - result / i;
    }
  }

  if (num > 1) {
    result = result - result / num;
  }

  return result;
}

module.exports = function (num) {
  validate(num, 'phi');
  return phi(num);
};