Why does this crash?

gistfile1.txt

import Foundation


func eratosthenes(n: Int) -> [Int]{
    
    var results = [Int]()
    
    for i in 0...(n-1){
        results.append(i+1)
    }
    
    for i in 0...(n-1){
        var number = results[i]
        var divides = number % i == 0
        if (divides) {
            results[i] = -1
        }
        println(number)
    }
    
    return results
}

eratosthenes(10)