Pi squared is nearly 10 (mihai.page)

My first thought was "well of course it is, since pi is a little larger than 3" but it was cool to see an actual derivation of how much pi squared differs from 10 as a nice, closed form series.

The author wants tau=2*pi, but in the Greek alphabet, tau has one vertical stroke, and pi has two.

So, visually in Greek, pi=2*tau would seem an improvement.

Oh, well.

The second fact, pi^2 ~= g, is famous enough that it has a separate section in Wikipedia [1].

[1] https://en.wikipedia.org/wiki/Mathematical_coincidence#Gravi...

I remember discovering that pi x 10^7 is very close to the number of seconds in a year while at uni.

One of my tutors was convinced this had to be more than coincidence, but I always figured it was just chance and a nice but sometimes useful shortcut...

I was a little disappointed that the upper range of gravity on earth only goes to 9.8337. Just a little more and there would have been somewhere on earth that was an exact match.

It would have been the ideal (if chilly) place to start a cult.

This first became apparent to me when I got a slide rule. Pi is often marked on the various scales and an x^2 scale is often nearby the x scale.

As an ex-physicist, pi^2 is 10. Like g.

I get it that this is a nice calculation with the Zeta function and everything, but 3 and a small something squared will be near 10 so it is 10.

If you don't unblock scripts from cdn.jsdelivr.net.cdn.cloudflare.net, the math code won't work.

I like the 4-5-6 theorem:

    pi^4 + pi^5 = e^6

Well, to five decimal places, anyway. Some other good ones:

    e^pi - pi = 20

    sqrt(2) ln pi = phi

There are also famous "almost integers" such as this one discovered by Ramanujan:

    e^(pi sqrt(163))

Which is an integer to 12 decimal places.

Edit: I just remembered I have public JupyterLite notebooks for both of these:

https://notebooks.oranlooney.com/lab/index.html?path=fake_ma...

https://notebooks.oranlooney.com/lab/index.html?path=heegner...

need a countdown for when it gets there

Pi^0 is exactly 1.

pi^2 ~ 10, well known to anyone who used slide rules.

987654321 / 123456789 = 8 (to the 7th decimal place) is another nice one

at this rate, pi square is close to 'g'

More advanced slide rules typically have a set of “folded” scales, that can sometimes save a calculation from ending up off scale. In theory, these should be offset by half the scale length, i.e. sqrt(10). However, since the folded scales also offer a convenient way to multiply with the offset factor, most slide rules offset them by π instead, since it’s almost the same as sqrt(10), and multiplication by π is a more useful thing to have around.

Also number of McDonald's in the world divided by number of McDonald's in US is close to pi. Within 1%.

6! is the number of minutes in 12 hours and the number of hours in a 30-day month.

> In the US and countries with a similar date format

Humm that's like 2 or 3 countries?