When considering what I would make for the contest, I thought about different equations related to circles and pi.  Somewhere along the line the equation C=2(pi)r came to mind and I had the idea to make two pie "r"s.  The rest came from there.  Due to personal kitchen limitations, I used Pillsbury refrigerated pie crusts, but I did make the filling from scratch.  This recipe can be made with your crust recipe and with any filling - this is more about the concept than the actual pie recipe.  Though the pie is pretty good.
Recipe:
3 Pillsbury refrigerated crusts (1.5 boxes) or your favorite crust recipe for 1.5 standard pies
6 large granny smith apples, peeled and sliced thin
1/3C brown sugar
1/3C granulated sugar
1/2T cinnamon
1/2t nutmeg
1/4C flour
heavy duty tin foil

1. Shape foil into "r" shaped pie pan, inside the pie pan you will bake in (it offers support and makes it easier, you can use the curve of the pan to shape the curve of the "r").  Make 2 "r" pans.
2. Preheat oven to 350 degrees.
3. Peel and slice apples, then combine with both sugars, spices and flour in large bowl.
4. Shape pie crusts into your pie pans.  I found it easiest to shape one piece of crust to the straight part of the "r" and a separate piece to the curved part.  Trim crusts so there is a few centimeters of crust hanging over edge of pan to seal.
5. Divide filling into pans.
6. Cover pie filling and secure the crusts at the edges.  Cut "pi" shaped vents in the pies. 
7. Bake in oven 40 minutes.
8. Enlist a photographer friend to take pictures of the pies for "pi day" contest.
9. Eat and enjoy!