Today, March 14 is a day to celebrate the number pi, the circle's circumference to its diameter --which is approximately 3.14. While it's unclear who actually invented pi, Welsh mathematician William Jones was the first to express pi as a ratio in 1707.  But pies have been around long before that --approximately in 9500 BC. 

So, let's celebrate this auspicious day with something that feeds our mind and body. 

Here are 7 outrageously delicious pies to dish up for your favorite math geek -- or anyone else who likes pies.