Several people emailed me that {\bf September 16, 2025}---written as {\bf 9-16-25} in the US---represents the integer side lengths of a right triangle. 

{\bf 9-16-25 is the only such triple that is also a valid date}. This kind of mathematical alignment only happens once every 100 years.  The next occurrence will be {\bf September 16, 2125.}

Since this is such a rare event, lets explore some more math-themed dates.

1) Pythagorean Triples That Work as Future Dates

Note that 9-16-25 is not a Pythagorean triple; however, 3-4-5 is. 

Here are upcoming dates that are both Pythagorean triples and valid calendar dates:

March  4, 2105 is 3-4-5

May 12, 2113 is 5-12-13

June 8, 2110 is 6-8-10 

July 24, 2125 is 7-24-25 (Darn---July 24, 2025 was recent and I missed it!) 

August 15, 2117 is 8-15-17 

I think that's it.  Recall that we need the month to be in \(\{1,\ldots,12\}\) and the day to be in \(\{1,\ldots,31\}\) with some exceptions: 

Thirty days has September, April, June, and November

All the rest have thirty-one,

Excepting February, fun!

And that has twenty-eight days clear

And twenty-nine in a Leap Year

(There are 24 versions of this poem at a website: see here.) 

2) Why Didn't Anyone Email Me About Earlier Dates?

I wonder why nobody emailed me on, say, March 4, 2005 (3-4-5).  That's a Pythagorean triple, but maybe it just looked like three consecutive numbers. Oh well.

And what about May 12, 2013 (5-12-13)? That's a really cool Pythagorean triple. Oh well.

3) Other Math-Related Dates Using Month, Day, {\it and} Year.

(So dates like Pi Day don't count---we want the {\bf full date} to be interesting mathematically.) 

a) Square days:

Dates where the full 8-digit number (MMDDYYYY) is a perfect square.

a1) September  27, 2025 is 9-27-2025 and \(9272025=3045^2\). 

Bonus: if you write it as 27-09-2025 then: \(27092025=5205^2\).

a2) Feb 2, 2084 is 2-02-2084 and \(2022084=1422^2\).

b) Palindrome days 

b1) March 11, 2030 is 03-11-30 might be the next one.

b2) I was hoping that Feb 2, 2022 (2-2-22) would be a Tuesday (Twosday) but alas, it was not.