Personalized Happy Pi Day Math Lover Party Youth T-Shirt. Pi Day math themed Youth T-Shirt - Black has pi symbols in a pie. Fun gift for a geek, math teacher, college math major or any math lover. Let the good times roll in a durable T-Shirt that takes kids from school to play in an amazing array of colors. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar.