3. 14159265359. . . . . . . . Flaunt your love for math and pi with this awesome t-shirt, featuring a pi symbol followed by the endless mathematical constant. This original Old Glory design is printed using cutting-edge direct-to-garment technology on a high-quality black, 100% cotton adult t-shirt. Designed in-house and printed to order, this is a one-of-a-kind sweatshirt for people with style to match.