Looping vs. Recursion

gistfile1.js

// solve(num) with isPrime(num) 
// approx. time to solve for 600 trillion: several hours
function solve(num) {
	var i = num - 1, result = num;
	for(;i>1;i--) 
	{
		if(num%i === 0) {
			if(isPrime(i))
			{
				result = i;
				break;
			}	
		}
	
	}
	return result;
}

function isPrime(num) {
	var i=2,
	result = true;
	for(;i<Math.ceil(num/2);i++) {
		if(num%i === 0) {
			result = false;
			break;	
		}
	}
	return result;
}
/*----------------------------------------------------------*/
// factor with recursion
// time to solve < .5s
function factor(num) {
	var i = 2, lim = Math.ceil(num/2), result=num;
	for(;i<lim;i++) {
		if(num%i === 0) {
			var p=num/i;
			if(p=factor(p)) {
				result = p;
				break;	
			}
		}
	}
	return result;
}