Personalized Happy Pi Day Math Lover Party Youth Long Sleeve T-Shirt. Pi Day math themed Youth Long Sleeve T-Shirt - Heather has pi symbols in a pie. Fun gift for a geek, math teacher, college math major or any math lover. youth long sleeve t-shirt. Shoulder-to-shoulder taping. Youth: S(6/8), M(10/12), L(14/16), XL(18/20)