Personalized Happy Pi Day School Math Party Long Sleeve T-Shirt. Happy Pi Day Long Sleeve T-Shirt - Pink math teacher or student apparel. Pre-shrunk 100% cotton 6.1 ounce long sleeve t-shirt. Double-needle stitched neckline and sleeves. Quarter turned. Shoulder-to-shoulder taping. Adult: S, M, L, XL, 2XL, 3XL