Happy 11/12/13, otherwise known as “tenty-one, tenty-two, tenty-three.”
Do your young children have trouble counting in the teens? Try making up Funny Numbers to help them! It’s a great habit to develop, because Funny Numbers will come in handy as mental math tools throughout their school math career.
If you’d like to make your own Happy Math Day post, check out the instructions here: Every Day Is Mathematics Day. And please share a link in the comments section below — I’d love to see what math holiday you invent!
Update: The numbers 11, 12, and 13 form an arithmetic progression. If that sounds too scary for your kids, check out Patrick’s bedtime math discussion Making Progress, Arithmetically.
Denise Gaskins' Let's Play Math 
Thanks for the pub, Denise! Tonight, my kids told me that they learned that today was a “Consecutive Number Day” at school. Of course, the dinner conversation focused around two questions: When is the next Consecutive Number Day? And how long till the one after that?
I guess it depends on whether we limit the word “consecutive” to the arithmetic progression with a difference of one. If we allow d to vary, we could have oodles of Consecutive Number Days in our lifetime. 🙂
Interesting that the sign says “Weird English Numbers Day” when here in England it’s not that date until next month! Here, we wrote yesterday’s date as 12/11/13, and we will have to wait until 11th December for 11/12/13.
My son likes that his 3 April 2005 birthday makes a Pythagorean triple the way we write it here – 3/4/5. That wouldn’t work over on your side of the Atlantic!
Today is a pretty cool date here, too – 13/11/13!
So funny! I guess the sign should say “Weird Americanglish Numbers Day”? Though of course, the numbers themselves (and the weird names for the “tenty” numbers) are the same on both sides of the water–it’s just that you don’t get the arithmetic progression until next month.