Finding out the factors of 2^(n)+1 ?

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I am trying to find out the factors for 2^(n)+1 and am adding the factors into a Listbox so for Smaller numbers it is showing the O/p for Larger Numbers like if we take "n" as a three digit number it's not showing the O/P
Here is my codeL:

Button Click()
{
a = Convert.ToUInt32(textBox1.Text);
            for (i = 0; i < a; i++)
            {
                c = c * 2;
            }
            c = c + 1;
            getfactors(c);
}
public List<double> getfactors(double number)
       {
           List<double> fs = new List<double>();
          for (double i = 2; i < number / 2; i++)
           {
               if (number % i == 0)
               {
                   fs.Add(i);
                    listBox1.Items.Add(i);
               }

           }
            return fs;
       }

Posted 11-Aug-10 19:13pm

Vigneshb6

Updated 11-Aug-10 21:22pm

LittleYellowBird

v3

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9852932254 · Answer 1 · 2010-08-11T21:26:00

C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsApplication16
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        double n,final;


        private void button1_Click(object sender, EventArgs e)
        {
            n = Convert.ToDouble(textBox1.Text);
            final = Math.Pow(2, (n + 1));
            textBox2.Text = final.ToString();
            for (int i = 1; i <= final; i++)
            {
                if (final % i == 0)
                {
                    listBox1.Items.Add(i.ToString());
                }

            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = "";
            textBox2.Text = "";
            listBox1.Items.Clear();
        }
    }
}

Peter_in_2780 · Answer 2 · 2010-08-11T21:46:00

Solution 2

The real problem is that well before you get to 2^100, you run out of numbers that can be accurately represented in an integer or double. If you want to go much beyond about 2^50, you'll need to use a BigInteger. Read up on range and precision as they apply to computer arithmetic.

Posted 11-Aug-10 21:46pm

Peter_in_2780

Comments

Vigneshb6 12-Aug-10 8:14am

Reason for my vote of 4
Yes ur Right