Uses CoffeeScript and Underscore.js to solve Project Euler #3 http://projecteuler.net/index.php?section=problems&id=3

CoffeeScript

# Sieve of Eratosthenes
# (an array loaded with prime numbers)
base = [2..10000]
primes = []
sieve = (set, pos) ->
    return false if pos >= set.length
    if set[pos] * set[pos] < set[set.length-1]
        primes = _.select set, ((num) ->
            return num if num == set[pos]
            return num % set[pos] != 0
        )
    return sieve(primes,pos+1)
sieve(base,0)

# Factor a number into its primes using out Sieve from above
factors = []
factorial = (primes, target, count) ->
    if primes[count] < target
        if target % primes[count] == 0
            factors.push(primes[count])
            target = target / primes[count]
        else
            count++
    if _.include primes, target
        factors.push(target)
    else
        factorial(primes, target, count)


factorial(primes, 600851475143, 0)
console.log(factors)