Added a function to get a precise number of prime numbers

Algorithms.lua

@@ -54,7 +54,53 @@ end
 
 --This function gets a specific number of primes
 function getNumPrimes(numberOfPrimes)
+	local primes = {};	--Holds the prime numbers
+	local foundFactor = false;
 
+	--If the number is 0 or negative return an empty table
+	if(numberOfPrimes <= 1) then
+		return primes;
+	--Otherwise the number is at lease 2, therefore 2 should be added to the list
+	else
+		primes[#primes + 1] = 2;
+	end
+
+	--We can now start at 3 and skip all even numbers, because they cannot be prime
+	possiblePrime = 3;
+	while((#primes < numberOfPrimes) and (possiblePrime >= 0)) do
+		--Check all current primes, up to sqrt(possiblePrime), to see if there is a divisor
+		primesCnt = 1;
+		--We can safely assume that there will be at least 1 element in the primes list because of 2 being added before the loop
+		topPossibleFactor = math.ceil(math.sqrt(possiblePrime))
+		while(primes[primesCnt] <= topPossibleFactor) do
+			if((possiblePrime % primes[primesCnt]) == 0) then
+				foundFactor = true;
+				break;
+			else
+				primesCnt = primesCnt + 1;
+			end
+			--Check if the index has gone out of range
+			if(primesCnt >= #primes) then
+				break;
+			end
+		end
+
+		--If you didn't find a factor then the current number must be prime
+		if(not foundFactor) then
+			primes[#primes + 1] = possiblePrime;
+		else
+			foundFactor = false;
+		end
+
+		--Advance to the next possible prime number
+		possiblePrime = possiblePrime + 2;
+	end
+
+	--Sort the array just to be neat and safe
+	table.sort(primes);
+
+	--Return the array
+	return primes;
 end
 
 --This is a function that returns all the factors of goalNumber