Need help with text boxes


I am working on a project and i just was wondering if this is possible in php and if you can give me some pointers.

I have 5 text boxes. Names txtbox1, txtbox2, and so on.

txtbox2 - txtbox5 are read only. txtbox1 is the only thing you can type in. txtbox1 can only have numbers typed into it (i have this part figured out). txtbox2 has to double the number from txtbox1 and show it in txtbox2, txtbox3 doubles txtbox2 and shows it, and so on to txtbox5. This is the part i need help with.

I just need to know if this is possible to have this done without having to click any buttons something like an excel spread sheet that would have this worked out ahead of time.

I hope i can get some help on this. I have done previous php work in the past but i have not been working with it so i am a bit rusty and would appreciate it if you could give me some code samples or point me to somewhere this has been done before.



update to the post.

For the text boxs i would need it to look like this

txtbox1 = 1 if i change this number all the other box with change
txtbox2 = 2 txtbox1 * 2
txtbox3 = 4 txtbox1 * 4
txtbox4 = 8 txtbox1 * 8
txtbox5 = 16 txtbox1 * 16