Today I Learned

[mfb]

Today I learned about a curious nearly-pattern in the decimal system:

$10^{14}-1 = 909,091 \times 109, 999,989$
$10^{24}-1 = 99,990,001 \times 9,901 \times 1, 010,099, 989,899$
$10^{36}-1 = 999,999, 000,001 \times 9,901 \times 100, 999,999, 999,999, 999,899$
$10^{38}-1 = 909,090,909,090,909,091 \times 109, 999,999, 999,999, 999,989$
$10^{39}-1 = 900,900,900,900,990,990,990,991 \times 1,109, 999,999 ,999,889$
$10^{48}-1 = 9,999, 999,900, 000,001 \times 99, 990,001 \times 1, 000,100, 009,999, 999,899 ,989,999$
$10^{62}-1 = 909,090,909,090,909,090,909,090,909,091 \times 109 ,999,999 ,999,999 ,999,999 ,999,999, 999,989$
$10^{72}-1 = 999999 000001 \times 99 990001 \times 9901 \times 101 \times 10,000, 999,999 ,989,998, 989,999 ,010,001, 010,000, 999,999 ,989,999$
$10^{78}-1 = 900,900, 900,900, 990,990, 990,991 \times 1 ,109,999, 999,999, 889,000, 000,000, 000,000 ,000,000 ,001,109, 999,999 ,999,889$

The numbers get too large for an exhaustive search, but two larger examples:
$10^{93}-1 = 900,900,900,900,900,900,900,900,900,900,990,990,990,990,990,990,990,990,990,991 \times 1,109,999,999,999,999,999,999,999,999,999,889$
$10^{196}-1 = 999,999,999,999,990,000,000,000,000,099,999,999,999,999,000,000,000,000,009,999,999,999,999,900,000,000,000,001 \times 900,900,900,900,990,990,990,991 \times 11,099, 999,999 ,999,000 ,999,999 ,999,988, 900,000, 000,011 ,099,999, 999,999, 000,999, 999,999 ,988,900 ,000,000, 011,099 ,999,999$

In each case all factors apart from the last one are prime numbers.

 

[Stavros Kiri]

Today I learned about a curious nearly-pattern in the decimal system:

$10^{14}-1 = 909,091 \times 109, 999,989$
$10^{24}-1 = 99,990,001 \times 9,901 \times 1, 010,099, 989,899$
$10^{36}-1 = 999,999, 000,001 \times 9,901 \times 100, 999,999, 999,999, 999,899$
$10^{38}-1 = 909,090,909,090,909,091 \times 109, 999,999, 999,999, 999,989$
$10^{39}-1 = 900,900,900,900,990,990,990,991 \times 1,109, 999,999 ,999,889$
$10^{48}-1 = 9,999, 999,900, 000,001 \times 99, 990,001 \times 1, 000,100, 009,999, 999,899 ,989,999$
$10^{62}-1 = 909,090,909,090,909,090,909,090,909,091 \times 109 ,999,999 ,999,999 ,999,999 ,999,999, 999,989$
$10^{72}-1 = 999999 000001 \times 99 990001 \times 9901 \times 101 \times 10,000, 999,999 ,989,998, 989,999 ,010,001, 010,000, 999,999 ,989,999$
$10^{78}-1 = 900,900, 900,900, 990,990, 990,991 \times 1 ,109,999, 999,999, 889,000, 000,000, 000,000 ,000,000 ,001,109, 999,999 ,999,889$

The numbers get too large for an exhaustive search, but two larger examples:
$10^{93}-1 = 900,900,900,900,900,900,900,900,900,900,990,990,990,990,990,990,990,990,990,991 \times 1,109,999,999,999,999,999,999,999,999,999,889$
$10^{196}-1 = 999,999,999,999,990,000,000,000,000,099,999,999,999,999,000,000,000,000,009,999,999,999,999,900,000,000,000,001 \times 900,900,900,900,990,990,990,991 \times 11,099, 999,999 ,999,000 ,999,999 ,999,988, 900,000, 000,011 ,099,999, 999,999, 000,999, 999,999 ,988,900 ,000,000, 011,099 ,999,999$

In each case all factors apart from the last one are prime numbers.

Is this for real?
[And I was wondering why my knowledge was incomplete! Seems I found what was missing! ... ]

 

[mfb]

You can check them with WolframAlpha or Dario Alpern's tool (which I used for factorization).
I got the idea from unique primes: If a prime is a unique prime with a period length p, then it is the largest factor of 10^p-1.

 

[Stavros Kiri]

You can check them with WolframAlpha or Dario Alpern's tool (which I used for factorization).
I got the idea from unique primes: If a prime is a unique prime with a period length p, then it is the largest factor of 10^p-1.

Thanks for the tips.

I got the idea from unique primes: If a prime is a unique prime with a period length p, then it is the largest factor of 10^p-1.

I am beginning to see the mechanism now

 

[nitsuj]

TIL that Canada has a "digitize stuff*" website, and recently just added a ton of stuff.

The site is called Canadiana and is "run" by CRKN - "The Canadian Research Knowledge Network is a partnership of Canadian universities, dedicated to expanding digital content for the academic research and teaching enterprise in Canada."

 

[Jonathan Scott]

TIL that there's always another way things can go wrong! Our orchestra had a great concert, but we couldn't get our cars out of the car park because all three of the automatic exit barrier systems were "out of order", and so was the "assistance" button (which just repeatedly said "please wait while your call is routed" for 10 minutes). Someone eventually found a phone number to contact, and after about 15 mins waiting in the rain someone came with a special key to manually set the barriers open. Still, it was a great concert (ended with Beethoven Symphony No 4).

 

[Tom.G]

For future reference, if those barriers are the the wooden arms that pivot upward they are VERY brittle wood and are extremely easy to break off, if you can't raise them manually (many can be raised). This is probably so there are not large damage claims when something goes wrong.

My wife and I learned this many years ago when exiting a parking structure on our motorcycle. For whatever reason, the arm came down between us on the motorcycle. Fortunately the sissy-bar prevented her from being swept off the back of the bike. Of course this called for a Manager to attend, who then tried to get us to pay for replacing the gate. He was dissuaded from this upon the suggestion of possible personal injury. During the discussion, a replacement gate was brought out and installed. We left and the whole situation was chalked up to 'Just one of those things.'

 

[Jonathan Scott]

TIL how to remove drink stains from my teak-finish coffee table, by ironing it (through a sheet of paper from a kitchen roll)!

After my son's recent birthday party, there were very obvious chalky-white patches on the coffee table, presumably from spilt drinks, which seemed to be totally unaffected by being wiped or polished, so I took some photos and emailed them to a local furniture restorer who replied saying he'd have to redo the whole surface. As that sounded quite drastic, I decided to risk a method I'd already seen described on the internet and try ironing the patches, very cautiously. It worked like magic, and I can't even tell where they were now.

So I I told the furniture restorer what I'd done and that I wouldn't be requiring his services after all!

 

[jtbell]

Today I learned that in some parts of the southern US, a heavy downpour of rain (which I think of as a "gully-washer") is called a "frog-strangler". Apparently those parts don't include the Carolinas, because I'd never heard or seen it in more than 30 years of living here. A local TV weather reporter mentioned it as being new to him.

For other regional terms see 11 Imaginative Regional Idioms to Describe Heavy Rain. "Turd-floater", anyone?

 

[Ibix]

For other regional terms see 11 Imaginative Regional Idioms to Describe Heavy Rain. "Turd-floater", anyone?

Raining stair-rods.
Nice weather for ducks.
Raining cats and dogs.

 

[Buzz Bloom]

TIL a concept new to me regarding the "essence of life".

I have been reading the 2009 book, The Greatest Show on Earth by Richard Dawkins, and I recommend it highly. It is an excellent entertaining well organized presentation of the enormous extent and variety of the evidence showing evolution is a fact. The last chapter (13), has sections titled with the quotes from Darwin's first edition of The Origin of Species. The "essence of life" concept is given in the section "Having Been Originally Breathed" (page 403).

The new to me concept is that the essence of life is information. The following is my interpretation of the Dawkins' exposition.

Originally there was the single form of life's information contained in DNA. Later immune systems became another form of life's information: antibody proteins which hold remembered information about past invasions of parasites, and later, inoculations. Later still neural systems evolved which learned and remembered valuable lessons in the form of positive and negative associations with good and bad stimuli. And in the current state of life, a fourth method of life evolved to retain important information is in the forms of language, first verbal and currently voluminously written.

 

[Hawkingo]

Today I learned about fermi paradox and the great filter ,the reasons why we haven't met any alien lifes yet .
from these videos

 

[MalcolmB]

TIL that a J47 jet engine igniter box is like a Model T Ford trembler coil on steroids.

 

[skyshrimp]

I learned that freezer burn and freeze drying is the same thing.

 

[Drakkith]

Today I learned about the website apollo17.org, where you can follow the mission in real time by listening to the actual audio communication between the spacecraft and the ground from before launch all the way to reentry. All 300+ hours of it. The website includes hours of video and thousands of photos from the mission as well. Highly recommended for anyone interested in space. Note that you are free to skip to any time-step, so if you want to listen to the reentry communications you don't have to wait for 2 weeks.

 

[Drakkith]

A quote that immediately made it into my top 10 favorite quotes:

"I know we're not the first to discover this, but we'd like to confirm, from the crew of America (Apollo 17 CSM), that the world is round."
- Gene Cernan, Commander of Apollo 17.

That quote is found in the link in my previous post just above at 4 hours 59 minutes 37 seconds into the mission.

 

[fresh_42]

A quote that immediately made it into my top 10 favorite quotes:

"I know we're not the first to discover this, but we'd like to confirm, from the crew of America (Apollo 17 CSM), that the world is round"
- Gene Cernan, Commander of Apollo 17.

That quote is found in the link in my previous post just above at 4 hours 59 minutes 37 seconds into the mission.

But how do we know that they didn't just fly perpendicular to the disc?

Regards, AD

 

[Drakkith]

But how do we know that they didn't just fly perpendicular to the disc?

Because then the photos would have shown the entire Earth and not just Africa and Antarctica.

 

[mfb]

Maybe all other continents don't exist? THEY just pretend they do to make Earth appear larger than it is!

 

[BillTre]

Maybe all other continents don't exist? THEY just pretend they do to make Earth appear larger than it is!

Oh no!
What happened to the continent I am on.
Maybe the Aliens stole it.

 

[DrGreg]

What happened to the continent I am on.

Sorry, the continent you thought you were on for the last year was just a dream.

 

[Ibix]

What happened to the continent I am on.

It's like running over a cliff in a cartoon. You can just keep going until you notice you're imagining your entire half of the globe.

 

[fresh_42]

What happened to the continent I am on.

It was demolished to make way for a new hyperspace bypass.

 

[jim hardy]

It was demolished to make way for a new hyperspace bypass.

thanks for all the fish...

 

[Ibix]

TIL that if I have an angle (in degrees) that may not lie in the range 0-360 (maybe I'm keeping track of orientation of a rotating object), and I want it to, the same formula works for values above 360 as below 0. For any $\theta$, then:
$$\theta'=\theta-360\times\mathrm{floor}\left(\theta\over{360}\right)$$
is guaranteed to be in the range $0\leq\theta'<360$, assuming that the floor function rounds numbers towards negative infinity.

 

[DrGreg]

$$\theta'=\theta-360\times\mathrm{floor}\left(\theta\over{360}\right)$$
is guaranteed to be in the range $0\leq\theta'<360$.

And if you want $-180\leq\theta'\leq180$, use $\mathrm{round}$ instead of $\mathrm{floor}$.

I'm being vague about ±180 because that will depend on what convention the $\mathrm{round}$ function follows (round to nearest integer).

 

[nitsuj]

A quote that immediately made it into my top 10 favorite quotes:

"I know we're not the first to discover this, but we'd like to confirm, from the crew of America (Apollo 17 CSM), that the world is round."
- Gene Cernan, Commander of Apollo 17.

That quote is found in the link in my previous post just above at 4 hours 59 minutes 37 seconds into the mission.

At 6m28s Evans - "One g? Just like sitting on the pad, isn't!"

 

[gmax137]

TIL, how to pronounce LaTeX. Something new everyday.

 

[Craftek_Ana]

TIL, Scientists have figured out how to confer a superpower, like those wielded by the mythical X-Men, at least to mice. Using nanoparticles that convert infrared (IR) light to visible light, researchers have given mice the ability to see in the dark. If the same technique works in humans, it could offer soldiers night vision without the need for goggles and possibly counter ailments that cause patients to gradually lose their sight.

Also, ArtificialIntelligence Software Outperforms Human Stylists at Fashion Week.

Exponential growth my friends, when do we hit the panic button?

Though like domino's once the chain effect is started there is most likely no stopping?

If this is only the beginning, what will the future be like?

 

[mfb]

Artificial Intelligence Software Outperforms Human Stylists at Fashion Week

OpenAI created an AI that can produce text so good that they are worried about the program getting abused (e.g. for homework, or creating fake texts assigned to a person who didn't write it).
News article

 

[Craftek_Ana]

OpenAI created an AI that can produce text so good that they are worried about the program getting abused (e.g. for homework, or creating fake texts assigned to a person who didn't write it).
News article

yeah,I read about that! :) Creative jobs were believed to be safe from AI or automation, it doesn't seem to be the case. We'll most likely need to merge to remain relevant in the future.

Directly or indirectly, AI or automation most probably is going to be the cause of wars. We have 7.7~ billion people who will be out of jobs in the decades to come, who need a source of income to survive. People are not happy campers when they haven't eaten.

 

[newbieli]

Really love this topic. Would like to share what I learned today. Guess what! a Japanese lady called Marie Kondo! I watched a show on Netflix called "Tidying Up with Marie Kondo". She has this << Link to commercial site deleted by Mentors >>[/B] to teach people how to tidy your bedroom, kitchen, etc. Really interesting show, recommend to you.

 

[Tom.G]

re. Those "Terms and Conditions" that all sites seem in love with. I just placed a small order with a site that had an honest and readable "Terms" page. Here it is, refreshing!

Important Notes Failure to Read This Is Normal This was not written by lawyers-there's loopholes somewhere. We reserve the right to do as we darn well please. Shipping: NO FREE SHIPPING-EVER. Shipping is generally via UPS. Please don’t jerk at me about the cost as the president of UPS no longer takes my calls/ UPS charges substantially more for residential delivery; If you don’t provide a VERIFIABLE company address, you will be billed at residential rates (UPS doesn’t care if you call your house a Company). Charges for other forms of transport are at my discretion and proportional to the hassle involved; I am not driving to the post office to save you 18 cents. On orders under ½ pound US Post is $3-5 cheaper. We can use this option if you prefer, but because there is no way to verify delivery, we will not re-ship lost orders at our expense. Make me $20.00 Richer Policy: Returns at the discretion of Arthur I. Platt Co. 20% re-stock or $20.00 whichever is larger. Orders under $50.00 must be paid with VISA/MasterCard or a $20.00 service charge added. International orders must be paid with VISA/MasterCard only. $20.00 per 1000 clips charge for certificate of compliance. Our Order Online System generates an email invoice/receipt. If you need it – SAVE IT. There is a $20.00 charge to make me look it up and re-email it. Phone orders paid with VISA/MasterCard will have receipt in the package. $20.00 charge to replace it.

 

[jtbell]

Today I learned that the Casio F-91W wristwatch, several of which I've worn over the years, is famous as the "Terrorist Watch" because al-Qaeda has commonly used it in making time bombs.

https://en.wikipedia.org/wiki/Casio_F-91W#Usage_in_terrorism

 

[Stephenk53]

Today I learned about fermi paradox and the great filter ,the reasons why we haven't met any alien lifes yet .
from these videos

According to some scientists there are other reasons as to why we haven’t seen any aliens. I don’t have a link though because I always forget to write them down