It's National Pi Day . . . as in the mathematical constant 3.14, not the kind you eat. But over the years, it's become that too: A bunch of pizza places have Pie Day deals. Here are a few national chains running promos . . .
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1.  Papa Johns has a buy-one-get-one deal. Rewards members who buy a large one-topping pizza can get a second one for $3.14.
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2.  Papa Murphy's has a deal on your NEXT pizza. If you buy one of their specials today, you'll get a coupon for 31.4% off your next order.
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3.  Cicis has one-topping pizzas for $3.14 with the promo code "PIDAY". Or you can get $3.14 off their buffet.
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4.  Blaze Pizza is selling 11-inch pizzas for $3.14.
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5.  Uno Pizzeria & Grill has $3.14 thin-crust pizzas.
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6.  7-Eleven rewards members can get pizzas for $3.14. It applies at Speedway and Stripes stores too.Â
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(CNETÂ /Â Good Housekeeping)