## Christmas Eve Numerology

Yes, today is Christmas Eve, but more importantly, it’s December 24. That bodes well for numerologists. Compliments of today’s date, here’s a number puzzle for you.

1. Write today’s date in the form mm/dd/yy.
2. Remove the slashes (/) to leave a six-digit number.
3. Add the digits of that number.
4. Divide the six-digit number from Step 2 by the sum you obtained in Step 3.
5. Take the square root of the result.

As your special bonus, insert the result of Step 5 where it says [number] in the URL below, then enter that URL into your browser. Enjoy! And happy holidays!

www.mathjokes4mathyfolks.com/[number].html

More math…

The result in Step 4 isn’t all that unusual. In fact, there are 120 dates in 2012 that, when the six-digit date is divided by the sum of those six digits, the result is an integer. (If the six‑digit date starts with a leading zero, just drop it.) But the result in Step 5 happens far less frequently — there are only 5 dates in 2012 for which Step 4 yields a square number. Can you find the other four?

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• 1. lukewalsh  |  December 26, 2012 at 7:02 pm

Thanks for the puzzle. I made a Desmos graph to help me find the others. https://www.desmos.com/calculator/hww6vavx2v Now I wonder about 2013 and other numerology that can be tested.

• 2. venneblock  |  December 28, 2012 at 12:48 pm

Wow, that’s cool stuff you did with the Desmos calc, Luke! Thanks for sharing. Eli Luberoff (the genius behind Desmos) and I will be presenting a session at the 2013 NCTM Annual Meeting in Denver. Perhaps we can share what you’ve done with attendees.

FYI, I popped all this stuff into Excel. I treated the year as a variable, so I can change that to investigate all dates for a particular year at one time. (I use a much larger version of this file to investigate all kinds of weird calendar numerology, but I stripped this version down just for the concatenation problem.) You can check it out here:
http://mathjokes4mathyfolks.com/files/MathDays-ConcatDivBySumGivesSquare.xls

• 3. lukewalsh  |  December 29, 2012 at 7:43 pm

Nice work with the Excel. I forget how powerful Excel can be. Here is a link to other Desmos graphs I have created. http://wallwisher.com/wall/desmos

The Math Jokes 4 Mathy Folks blog is an online extension to the book Math Jokes 4 Mathy Folks. The blog contains jokes submitted by readers, new jokes discovered by the author, details about speaking appearances and workshops, and other random bits of information that might be interesting to the strange folks who like math jokes.

## MJ4MF (offline version)

Math Jokes 4 Mathy Folks is available from Amazon, Borders, Barnes & Noble, NCTM, Robert D. Reed Publishers, and other purveyors of exceptional literature.