Cutie Pi
I just digitized this for a t-shirt. Send me a pm with your email and I will send it to you.
I ate some pi and it was yummy.
I don't know if any of these will work for you or not.
I found some based on Calculus but unfortunately, they are on a site that offers illegal designs...so they cannot be posted here.
If my embroidery machine were not in the shop -- I would digitize a math problem for you -- but I have no way of testing the design right now.
I guess they're more chemistry really but you may like some from Dave Johnsen's page.
If you do ye olde google thing you'll also come up with lots, such as... http://www.kidsmathgamesonline.co...