It's the annual celebration that mimics the first three digits of the mathematical constant pi, 3.14.
If you aren't aware of this Internet-fueled holiday, March 14 references the ratio between a circle's circumference and its diameter, an irrational number that can be rounded out to about 3.14. So, you can celebrate Einstein's birthday and a crazy-long decimal with your favorite type of pizza or pie.
Thursday, March 14, is Pi Day 2019, and plenty of restaurants have special pie and pizza deals. "I would pie-ly recommend it".
Cici's Pizza: Buy one adult buffet and a drink and receive a second adult buffet for free.
White Castle: With a coupon, get a Breakfast Slider combo for $3.14.
Recently, Pi Day has become a fun way for companies to promote deep discounts on pies and pizzas.More news: National Football League draft prep: Biggest takeaways from Kyler Murray's pro day
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Marie Callender's: Coupon for free slice of pie with adult entree purchase.
Guests can buy one thin crust pizza and get a second one for $3.14, and members of the Pie Life loyalty club get a $2 reward for their next visit.
The meal kit service is offering a pretty sweet Pi Day deal for first time subscribers: free dessert for a year! This offer is only available on March 14.
Salt and Straw: The popular artisan ice cream shop has a pie infused flavor that's ideal for Pi Day: wild foraged berry slab pie. Unfortunately, this deal does not include cheesecakes or seasonal fresh fruit pies.
7-Eleven stores will offer a whole pizza via the chain's 7NOW app for $3.14.
Whole Foods throughout Bay Area: Large pies will be selling for $3.14 less. They will have apple, apple blueberry, coconut cream, chocolate cream, key lime and lemon meringue.