The design on this polo-style shirt looks like a highway route sign. The top of the sign reads ROOT and the bottom shows a square root symbol over the number 4356. The square root of 4356 is 66... so this sign reads "Root 66". This is a funny geek t-shirt spoof of Route 66.
Shown here on a polo style shirt in black, this geek apparel design is available on a wide variety of other clothing colors and styles. The design is distressed for a vintage look. Get this funny t-shirt for the math geek in your life!