Lecture Notes 07 July 2014

import java.util.*;

public class Func
{
  public static int sumDigits (int n)
  {
    int sum = 0;
    while (n > 0)
    {
      sum += n % 10;
      n = n / 10;
    }
    return sum;
  }

  public static int revNum (int n)
  {
    int rev_num = 0;
    while (n > 0)
    {
      rev_num = rev_num * 10 + (n % 10);
      n = n / 10;
    }
    return rev_num;
  }

  public static boolean isPalindromic (int n)
  {
    return (n == revNum (n));
  }

  public static int sumDiv (int n )
  {
    int sum_div = 0;
    int limit = n / 2;
    for (int i = 1; i <= limit; i++)
    {
      if (n % i == 0)
        sum_div += i;
    }
    return sum_div;
  }

  public static boolean isPrime (int n)
  {
    int limit = (int) (Math.sqrt (n)) + 1;
    for (int i = 2; i < limit; i++)
    {
      if (n % i == 0)
      {
        return false;
      }
    }
    return true;
  }

  public static void main (String[] args)
  { 
    /*
    // Create a Scanner object
    Scanner sc = new Scanner (System.in);

    // Prompt the user to enter a positive number
    System.out.print ("Enter a number: ");

    // Read the number
    int n = sc.nextInt();

    // Sum the digits of the number
    System.out.println ("Sum digits = " + sumDigits (n));

    // Reverse the number
    System.out.println ("Reverse number = " + revNum(n));

    // Check if the number is palindromic
    if (isPalindromic (n))
      System.out.println (n_orig + " is palindromic");
    else
      System.out.println (n_orig + " is not palindromic");

    // Sum divisors of a number
    if (n == sumDiv (n))
      System.out.println (n + " is a perfect number");
    else
      System.out.println (n + " is not a perfect number");

    // Test if the number is prime
    if (isPrime (n))
      System.out.println (n + " is prime");
    else
      System.out.println (n + " is not prime");
    */


    // obtain amicable numbers less than 10000
    for (int p = 1; p < 10000; p++)
    {
      int sumP = sumDiv (p);
      for (int q = p + 1; q < 10000; q++)
      {
        int sumQ = sumDiv (q);
	if ((p == sumQ) && (q == sumP))
	{
          System.out.println (p + "  " + q);
	}
      }
    }
  }
}