Goldbach's conjecture in JavaScript - using Recursion

goldbach_recursion.js

/* Goldbach's conjecture in JavaScript - using Recursion
 *
 * author: Igor Hercowitz
 */


function isPrime(n) {
   if (n % 2 === 0) return false;

   var sqrtn = Math.sqrt(n)+1;
 
   for (var i=3; i < sqrtn; i+=2) {

      if (n % i === 0) return false;
   }

   return true;
}

function primeList(a) {
   if (isPrime(a)) return a; else return false;
}

function generateNumbers(initial) {
    var num = (initial % 2 === 0)?(initial -1):initial;
    var list = []
    for (var i = num; i > 3; i-=2)
        list.push(i);
    list.push(3,1);
    return list;

}

function calculate(initial, list, results) {
   if (list.length === 0) return results;

   var item = list.shift();    
   var itemPairIndex = list.indexOf(initial - item);
   if  (itemPairIndex !== -1) {        
     var itemPair = list.splice(itemPairIndex,1)
     results.push(item+"+"+itemPair);
   } 
   return calculate(initial, list, results);         
    
}

function goldbach(initial) {
    var pairs = [];
    var list = generateNumbers(initial).filter(primeList);
    return calculate(initial, list, []);
}

var initial = 10000;
print(initial+" can be represented as: "+(goldbach(initial)));