Thread: More number theory

Some code examples. I think I will focus on more useful and practical code from now on. I'm pretty sure noone cares about number theory. Can you guys give me a little insight as to how to structure and guide my studies?

//Jeremiah A. Walker
//Euclidean algorithm to get the GCD(Greatest Common Denominator) of two numbers
public class gcd
{
	public static long Euclid(long a, long b)
	{
		if(b == 0)//if b is 0, return a
			return a;
		else//if b\ is not 0 find GCD
			return Euclid(b, a % b);
	}//end Euclid
 
	public static void main(String[] args)
	{
		long n0 = Long.parseLong(args[0]);
		long n1 = Long.parseLong(args[1]);
 
		long res;
 
		if (n0 > n1)
			res = Euclid(n0, n1);
		else if(n1 > n0)
			res = Euclid(n1, n0);
		else 
			res = n0;
		System.out.println(res);
 
	}//end main
}//end gcd

//Jeremiah A. Walker
//An integer is said to be a perfect number if its factors add up to the integer
//For instance 6 is perfect because 1+2+3 =6 
//Write a program that can determine if a number is perfect and print all the perfect numbers between 0 and x
 
import java.util.*;//scanner and arraylist
 
public class pnum
{
	public static void main(String[] args)
	{
	Scanner input = new Scanner(System.in);
	System.out.println("Give me an integer between 2 and 10,000:  ");//asks user for a number
	int number = input.nextInt();//reads user input
	int total = 0;//total, stores the sum of the factors of the user input number
	ArrayList<Integer> factor = new ArrayList<Integer>();
 
	for(int i = 1; i < number; i++)
	{
		if(number % i == 0)
		{
			total += i;
			factor.add(i);
		}//end if
	}//end for
		System.out.print("1");
		for(int i = 1; i < factor.size(); i++)
		{
			System.out.print(" +" + factor.get(i));
		}//end for
		System.out.print(" = " + total + "\n");
		if(total != number)
			System.out.print("This number is not perfect.\n");
		else
			System.out.print("This number is perfect.\n");
	}//end main
}//end pnum

//Jeremiah A. Walker
//Print all the perfect numbers from 2 to 10000
//Check each one 
import java.util.*;
 
public class pnum2
{
	public static void main(String[] args )
	{	
		for(int n = 2; n<=10000; n++)
			if(isPerfect(n)) 
				System.out.println(n + " is perfect");
 
	}//end main
 
 
	private static boolean isPerfect(int n)
	{
		int total = 0;
		for(int i = 1; i < n; i++)
			if( n % i == 0) 
				total += i;
			return (total == n);
	}//end isPerfect
}//end class pnum2

If you like this kind of stuff, you will love Project Euler