If you want an interesting challenge, head out with your camera and search for numbers and letters or better still, objects that look like numbers and letters. You'll be impressed with how many you'll actually find and when they're put together they can make an interesting panel to hang on your wall. All you need is your camera, a good imagination and some decent weather!
If you're looking for ideas, a lighthouse can be used as a number one, chimneys can look like a number 11 and a traffic light can be a 3 or and E depending on the direction they're facing.
When we say photograph numbers/letters, you can take this literally or you could put your imagination to the test and look for them in places other people wouldn't think to look.
If you have a door number start with that then take a walk up your street and into your town snapping shop signs, adverts and road signs. Make sure you fill the frame with what you find and watch out for reflections and glare bouncing off shiny door numbers.
When you're ready to give your grey cells a bit of a work out start looking for objects that look like numbers and letters. You may need to stand and imagine what the object looks like flipped the other way or crop into a part of it to get the number you're looking for but with a little work with your imagination you'll soon be on your way. Make sure you take a quick look at what's surrounding your subject as a busy background won't make the number jump out of the frame. Try using a large aperture to throw background out of focus leaving all attention on your object.