Tuesday, March 20, Seattle seafoodies will be making plans to stop in at an Ivar’s, to celebrate the 107th birthday of its “flounder” Ivar Haglund. It’s not just a marketing ploy, though Ivar was known for them. People just like celebrating Ivar’s birthday. (“Last year we served the largest number of guests in a single day in our company’s history,” says Ivar’s president Bob Donegan.)

How entwined is Ivar’s with Seattle? Here’s Rainn Wilson welcoming new Seahawk Matt Flynn on Twitter: “Dear Matt Flynn, the city of Seattle welcomes you! Enjoy your stay. Try the fish & chips @ Ivars! Throw lots of TDs, mmK?”

(To which @IvarsClam replied to Wilson: “Thanks for recommend. Hoping 2 see u in Seattle soon Come on by and try on the clam suit. You’ll never go back.”)

Here are the full details on Ivar’s 107th Shellebration, but the main thing is the offer of a buy-one-get-one-$1.07-entrée at all of Ivar’s full-serve restaurants–Ivar’s Acres of Clams on Seattle’s waterfront, Ivar’s Salmon House on north Lake Union, and Ivar’s Mukilteo Landing on Possession Sound–and 25 Seafood Bars across Washington state.

You do have to “exclaim ‘Happy Birthday, Ivar!'” we are told, before you can get the second entrée from the birthday menu (full-service, Seafood Bar) for $1.07. There’s more in the way of birthday presents, including a $107 gift card for one lucky  entrant in the “Ivar Haglund Birthday Video Contest.” Post yourself singing happy birthday to Ivar to their Facebook page by March 21, and you’ll be in the running. Don’t overthink it. Fire up the iPhone and go.