mathball/lib/stormer/index.js

A JavaScript library for Competitive Programming

"use strict";

/* Function to check if number is a stormer number
    Function name: isStormer()
*/

var validate = require("../validation/positive-integer");

function maxPrimeFactor(inp) {

    var maxPrime = 1;

    var temp = inp;
    //testing for all multiples of 2
    while (temp % 2 === 0) {
        maxPrime = 2;
        temp = temp / 2;
    }
    //for the remaining odd numbers. Note that prime numbers will remove their non-prime multiples BEFORE any
    //non- prime number can appear
    for (var i = 3; i <= temp; i += 2) {
        while (inp % i === 0) {
            maxPrime = i;
            inp = inp / i;
        }
    }
    return maxPrime;
}

exports.check = function (n) {

    validate(n, 'isStormer');
    var largPFactor = maxPrimeFactor(n * n + 1);

    return largPFactor >= 2 * n ? true : false;
};