Today I Learned

[dlgoff]

This man was stung seven times by murder hornets while trying to save Vancouver Island's honeybees
https://www.cbc.ca/television/this-...o-save-vancouver-island-s-honeybees-1.5971560

This makes me cringe, as I was hospitalized once from bumblebee stings. Freely flowing liquids from both ends simultaneously.

 

[collinsmark]

Is there a thing with cicadas and primes?

Oh, yes.

The Cicada’s Love Affair With Prime Numbers​

 

[mfb]

Today I found two examples of weird large derivatives appearing:
A particle bouncing inside a convex region can be a chaotic system. But the motion cannot be chaotic if the 553rd derivative of its boundary is continuous (Lazutkin, 1973). Later work improved that requirement down to the 6th derivative. Discussed by @john baez in 2016: Blog article

If you take the Minkowski sum ($\{a+b:a\in A,b\in B\}$) of convex subsets A, B of $\mathbb{R}^2$ with real-analytic boundaries then the boundary of A+B is guaranteed to be "6+2/3" times differentiable.

 

[strangerep]

I do not feel good about anything with more than 4 legs.
Is there a thing with cicadas and primes?

Cicadas are cute and harmless -- as a child we used to catch them, trying to collect as many different varieties as possible. There were quite a few names, but now I only remember "Green Grocer", "Black Prince", "Yellow Monday(?)", "Pizz Whacker" (don't ask) ...

 

[rsk]

Today I learned that if you don't have a spare CR2032 battery handy, two CR2016s, stacked, will do the job nicely.

 

[phinds]

That one of the weirdest things in numerology that I've ever seen is this:

111,111,111 x 111,111,111 = 12345678987654321 [counts up 1 to 8 then down 8 to 1 but with a 9 in the middle)

What has me flummoxed is NOT the math so much as who in hell every happened to SEE it ? I mean, whoever it was has WAY too much spare time on their hands.

 

[jedishrfu]

I think this comes from playing with 1 x 1 = 1, 11 x 11 = 121, 111 x 111 = 12321 ... so naturally someone would extend the sequence to the limit of disbelief.

 

[Keith_McClary]

whoever it was has WAY too much spare time on their hands.

         111111111
        x111111111
        __________
         111111111
        111111111
       111111111
      111111111
     111111111
    111111111
   111111111
  111111111
 111111111
_________________
 12345678987654321

 

[Keith_McClary]

 

[Janus]

That one of the weirdest things in numerology that I've ever seen is this:

111,111,111 x 111,111,111 = 12345678987654321 [counts up 1 to 8 then down 8 to 1 but with a 9 in the middle)

What has me flummoxed is NOT the math so much as who in hell every happened to SEE it ? I mean, whoever it was has WAY too much spare time on their hands.

It's part of a pattern:
11 x 11 = 121
111 x 111 = 12321
1111 x 1111 = 1234321
etc.

 

[DrGreg]

It's part of a pattern:
11 x 11 = 121
111 x 111 = 12321
1111 x 1111 = 1234321
etc.

Or an even more general pattern$$\begin{align*}
(x+1)^2 &= x^2 + 2x + 1 \\
(x^2+x+1)^2 &=x^4 + 2x^3 + 3x^2 + 2x + 1
\end{align*}
$$etc.

 

[fresh_42]

That one of the weirdest things in numerology that I've ever seen is this:

111,111,111 x 111,111,111 = 12345678987654321 [counts up 1 to 8 then down 8 to 1 but with a 9 in the middle)

What has me flummoxed is NOT the math so much as who in hell every happened to SEE it ? I mean, whoever it was has WAY too much spare time on their hands.

Yes, but this is what can be found playing with sequences of ones. However, who the heck found that:
$$2^n+7^n+8^n+18^n+19^n+24^n=3^n+4^n+12^n+14^n+22^n+23^n \text{ for } n =0,1,...,5$$

 

[jedishrfu]

Many genius level mathematicians have an incredible computation skill.

I remember the scene in the Ramanujan movie where one of the Oxford dons could do fast calculations and battled with Ramanujan to test his skill or something like that.

There also was that savant David Tamett who could do remarkable feats of calculation and memorization.

 

[DaveC426913]

Today I learned that if you don't have a spare CR2032 battery handy, two CR2016s, stacked, will do the job nicely.

Only in devices that will tolerate a doubling of the voltage.

 

[Ibix]

Many genius level mathematicians have an incredible computation skill.

You know that puzzle with two trains that start 70km apart and travel in opposite directions, one at 30kph and one at 40kph and a fly that flies backwards and forwards between the trains at a constant 80kph (it's one o' them rocket propelled flies) - how far has the fly traveled when the trains meet? There's a popular theory that mathematicians given this problem spot that there are two geometric series to sum, but physicists shy away from the computation, and then note that the trains meet in an hour so the fly also travels for an hour, hence flies 80km.

There's a story of someone who decided to test that theory, and the first person he happens across is John von Neumann. He quickly lays out the problem and von Neumann says instantly "80km". The guy is a little crestfallen and explains to von Neumann that he had expected him, as a mathematician, to take the series sum solution rather than the easy way. "Ah," says von Neumann, looking a little embarrassed. "You're right, there is an easier way to do it."

 

[rsk]

Only in devices that will tolerate a doubling of the voltage.

I did wonder about this, but it seems to be ok.

FWIW it's the button part of a wireless doorbell in my parents' home.

 

[DaveC426913]

I did wonder about this, but it seems to be ok.

FWIW it's the button part of a wireless doorbell in my parents' home.

Is their doorbell twice as loud now?

 

[rsk]

Is their doorbell twice as loud now?

Button part. The bell part still has its regulation batteries. But now I'm scared that the post man or delivery man might get hurt when pushing the button

(nah, 6V not going to hurt anyone, right?)

 

[Ibix]

FWIW it's the button part of a wireless doorbell in my parents' home.

Several years ago I learned that if you buy a wireless doorbell and select one of the sixteen channels it can transmit on at random, your neighbour will also buy the same model and select the same channel. Neither of you get loads of unexpected visitors, so the one who actually has a visitor will usually be ready and let them in before the other has found his front door keys. So it will take some months for you to work out the cause of occasional "nobody there" bell rings...

 

[pbuk]

Only in devices that will tolerate a doubling of the voltage.

Yeah, don't try this at home kids. Youd be better off jamming some aluminium foil wrapped round cardboard in there.

 

[mfb]

However, who the heck found that:
$$2^n+7^n+8^n+18^n+19^n+24^n=3^n+4^n+12^n+14^n+22^n+23^n \text{ for } n =0,1,...,5$$

What computer found that?
Prouhet–Tarry–Escott_problem

 

[rsk]

Only in devices that will tolerate a doubling of the voltage.

Yeah, don't try this at home kids. Youd be better off jamming some aluminium foil wrapped round cardboard in there.

Heeding these warnings, I decided to rummage through my foreign coin collection to see if I had anything approximately battery sized and thin enough and yes, it works!

The odd thing about this is that the coin is a US dime and the only time I ever set foot in the USofA was to transit through Atlanta airport. I don't even know what a "dime" means.

But anyway, it's working, presumably at 3V instead of 6V and with a spare battery returned to the blister it came from.

 

[jedishrfu]

A penny is one cent, a nickel is five cents, dime is ten cents, a quarter is 25 cents, and a half dollar is 50 cents vs a US dollar which is 100 cents.

There may be some other more obscure US coins that are no longer in use But I don’t remember them.

oh yeah we even have a two dollar bill which my coworker would use to be different when shopping. They weren’t popular and caused havoc at the cash register because there weren’t enough drawer slots for all the common bills 1, 5, 10, and 20 and this one.

 

[rsk]

Interesting fact, Cuba actually has notes worth 3 pesos. 1, 3, 5, 10, 20, 50 ... no 30s or 300s, just the 3.

This applied in both their CUP and CUC, but the latter (the convertible one pegged to the US$) has recently been removed from circulation - the currency, not just the 3 peso note.

 

[JT Smith]

But anyway, it's working, presumably at 3V instead of 6V and with a spare battery returned to the blister it came from.

Hang onto that extra battery. The cr2016 is less than half the capacity of the '32 so you'll be fiddling with it a lot sooner than if you just went to the store and bough the right battery.

 

[berkeman]

dime is ten cents

A dime is also an assist in basketball...

https://basketballword.com/in-basketball-what-does-dropping-dimes-mean-explained/#

Many of us know basketball terminology but have no clue where terms may have come from or how they originated. Such is the case with the saying dropping dimes.

What does dropping dimes mean in basketball? In basketball, the term dropping dimes refers to an assist, in which a player will make a pass to a teammate which leads to scoring a basket. The dime we are talking about is the ten-cent coin that was needed to use a payphone. Putting a 10 cent coin into the payphone was known as dropping a dime.

A dime may be an easy or difficult pass that would lead to a score in basketball. The saying would usually come from the player that acquired the assist, or by fans watching the player do so. “He’s dropping dimes”.

 

[JT Smith]

Interesting fact, Cuba actually has notes worth 3 pesos. 1, 3, 5, 10, 20, 50 ... no 30s or 300s, just the 3.

Apparently the U.S. used to have a three cent coin, way back when. Half penny, two cent, and twenty cent coins as well.

 

[rsk]

Hang onto that extra battery. The cr2016 is less than half the capacity of the '32 so you'll be fiddling with it a lot sooner than if you just went to the store and bough the right battery.

Just as soon as it stops raining.

 

[mfb]

A penny is one cent, a nickel is five cents, dime is ten cents, a quarter is 25 cents, and a half dollar is 50 cents vs a US dollar which is 100 cents.

Is the half dollar actually used?
There are 1 dollar coins.
https://en.wikipedia.org/wiki/Dollar_coin_(United_States)

For some reasons your 5 cent coin is larger than the 10 cent coin, and apparently 50 cent is larger than 1 dollar as well.

 

[JT Smith]

Is the half dollar actually used?

Not very often. Dollar coins are also not seen frequently. For that matter, who uses cash anymore? Since the pandemic shut down I think I've paid in cash about five times.

The $2 paper bill is also kind of rare. You can get them at the bank if you want. A friend owed me a couple hundred dollars and paid me with 100 of them just for fun!