I just bought two prints from Green Chair Press. They are limited edition prints, made with wood type (I like wood type -- we hung an old wooden type block to give our apartment number). I found this store via sfgirlbybay's website.
I plan to hang them together, probably in light wood frames. I think the colors will work nicely together. There are also several with just letters, but I like the way the numbers overlap. Plus, they seem appropriate for a math teacher, yes?