Pi is a mathematical constant and appears in many formulas of mathematics and physics. It is nearly equal to 3,14159 and is represented by the Greek Letter ‘Pi’. The hoodies are nice birthday or Christmas gifts for students, teachers, geeks or nerds. If you are interested in 3.14, mathematics, physics, algebra, math, symbols, numbers, letters, science, math tees, teaching, pi day, Halloween or school, you might like these shirts.