Yesterday I saw this fantastic post on twitter:
Since my older son leaned calculus last year, I thought it would be fun to run through the 9 equations with him, and then focus on the one about the logarithm of N!
Here are his thoughts on the equations:
Now we explored the one about the log of N! in a bit more depth – I was happy that after a few months off from calculus some of the main ideas still seem to have stuck around:
Finally, we went to Mathematica and explored the formula a bit more to see how good it was. We then wrapped up by looking at the Wikipedia page for Stirling’s approximation.
I’m glad to have gotten 2 days worth of laughs from Skinner’s post. Happy that it was also a fun starting point for a lesson, too 🙂
Mike's Math Page 
That’s definitely unlawful. At least the other 8 are equalities!
BTW if you want calculus-related math jokes, check out “Fun with very large numbers”, https://arxiv.org/abs/1105.3943 .