quick-primefactors

quick-primefactors

Compute a number's prime factors as quickly as possible, using a cached Sieve of Eratosthenes. This is especially helpful to lookup many numbers' factors one after another.

Install

$ npm install quick-primefactors

var pf = require('quick-primefactors');

Usage

// Simple examples
console.log(pf(47)); // [47]
console.log(pf(48)); // [2, 2, 2, 2, 3]
console.log(pf(51)); // [3, 17]
console.log(pf(100)); // [2, 2, 5, 5]

// More challenging examples
console.log(pf(3000000)); // [2, 2, 2, 2, 2, 2, 3, 5, 5, 5, 5, 5, 5]
  // took less than 0.5 seconds

console.log(pf(2987000)); // [2, 2, 2, 5, 5, 5, 29, 103]
  // took less than 0.0005 seconds

This module uses a cached Sieve of Eratosthenes for constant time lookup. A new one will be automatically generated if the number you're testing is larger than the currently cached sieve's upper bound.

For best results, lookup your highest number first. This will ensure the sieve is only calculated a single time.

Tests

To run the test suite, first install the dependencies, then run npm test:

$ npm install
$ npm test

To test code coverage:

$ npm run cover