If you've been around for a while, you probably know that all Mastercard credit cards start with 5, and all Visa cards start with 4. Beyond that, there's more math than you realized in credit card numbers. They are not randomly generated. For example, the last number is what's called a "check digit." It's there to make sure the other numbers are correct.

You don’t select this last digit, it is deterministic. The exact mathematic formula for its generation was invented by Hans Peter Luhn, an engineer at IBM in 1954. Originally patented, the algorithm is now in the public domain and a Worldwide standard ISO/IEC 7812-1
    
Obviously, with just a single check digit, not all errors can be detected (there’s a one in ten chance of a random number having the correct check digit), but the Luhn algorithm is clever in that it detects any single error (getting a single digit wrong), such as swapping the 9 with a 6 in the above example. It also detects almost all* pair-wise switching of two adjacent numbers. These errors are typical common errors people make when transcribing card numbers, so the check digit does a good thing.

An added side benefit is that, as discussed above, there is only a one in ten chance that a randomly generated number has the correct check digit. This provides a small amount of protection from hackers or poorly educated crooks who might attempt to randomly generate and guess credit card numbers.

See the formula for the check digit in action at DataGenetics, and more about how credit card numbers work. Link -Thanks, Nick!

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This is the morning rush hour in Beijing. Good luck getting off the train at your stop, because you might get pushed back in! -via reddit

Is this swimsuit ready to bite, or has it been bitten? Either way, it will remind everyone at the beach to be on the lookout for sharks! Bad Aby of Bad Aby Designs makes these to order to fit the customer, with optional features. Link -via Laughing Squid

Voice actor Nick Landis took his girlfriend Erika to Walt Disney World a couple of weeks ago to propose to her. As the big moment was being photographed, this poor soul stepped in front and immediately realized what he did. It's a moment that will live forever, because Erika posted it to reddit, where it made the front page this morning. But that was just the beginning. The same tourist has apparently photobombed other significant events, which made him an instant meme called InTheWayGuy. Link

While we speculate on what biological forms any extraterrestrials may take, several experts believe that we are more likely to encounter advanced forms that can reach out to us. Maybe even artificial intelligence. When any intelligent species reaches the point of space travel, it shouldn't be too long -on a cosmic scale- before they can build machines that are smart enough to both replicate and improve themselves. And travel through space.  

“If we build a machine with the intellectual capability of one human, then within 5 years, its successor is more intelligent than all humanity combined,” says Seth Shostak, SETI chief astronomer. “Once any society invents the technology that could put them in touch with the cosmos, they are at most only a few hundred years away from changing their own paradigm of sentience to artificial intelligence,” he says.

ET machines would be infinitely more intelligent and durable than the biological intelligence that created them. Intelligent machines would be immortal, and would not need to exist in the carbon-friendly “Goldilocks Zones” current SETI searches focus on. An AI could self-direct its own evolution, each "upgrade" would be created with the sum total of its predecessor’s knowledge preloaded.

Read what other minds are thinking along these lines at The Daily Galaxy. Link -via mental_floss

It's quite impressive to know that Alex Santoso received his PhD at only 25. But it's not a world record. There are outliers, childhood prodigies, who skipped grades left and right to get a doctorate at unbelievably young ages, like Ruth Lawrence.

In 1985, at the tender age of 13, Ruth Lawrence graduated from Oxford University with a bachelor’s degree in Mathematics. The next year, she got a second degree, this time in Physics, which was followed by a PhD in Mathematics in 1989 when she was just 17. After spending some time at Harvard as a junior fellow and working at the University of Michigan as an associate professor, Lawrence moved to Israel. There, she became an associate professor at the Hebrew University of Jerusalem.

But she wasn't the youngest ever. Read about ten such young doctors. Link -via the Presurfer

Just the thought of brownies with a cheesecake swirled into the mix makes me drool. Redditor qwertymodo said, "Every single time I've made cheesecake swirl brownies, I've wanted to do this. I finally did." I'm glad, too! This is a work of art. So to speak. Link

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Believe it or not, women come in a wide variety of personalities with a wide range of interests -just like men. You'd never know that by the arguments on some internet forums about whether a particular woman is a "geek" or a "fake geek girl" -or even whether such a thing as a female geek exists. Meanwhile, there is a growing group of women who have heard it all and want you to know they have nothing to prove. Geek girls are just what they are, and the song "Nothing to Prove" by The Doubleclicks says it well. In this video, women -and young girls, too- contribute video clips that say what they want to add to the conversation. I had to watch this twice, because the first time I kept stopping the video to read all the signs. The second time I wanted to hear the song in one piece. You can submit a picture or story, too, at the Tumblr blog Geek Girls have #Nothing to Prove. Link -via Metafiter 

When Sheyne and Glenn got married, they had a scientific Victorian steampunk octopus wedding, complete with a robot ring bearer!

We had a robot ring bearer built by our friend, Grant. He was named Heisenborg, and he delivered our wedding rings in a test tube and Erlennmeyer flask. Later in the evening, using the remote control, Grant had Heisenborg danced with a few friends on the dance floor.

Their friend Grant is Grant Imahara from Mythbusters. He was dressed in steampunk regalia like the other guests. You can see many photographs with other Victorian details at Offbeat Bride. Link -Thanks, Coyote!

(Image credit: Pixie Vision Photography via Flickr)

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Man with a Mission is a Japanese rock and dance band whose members wear wolf masks. Really. Due to popular demand, the We Are Family towels sold at their concerts are now available from the band's online gift shop (and they may even cost less than the ad says, but my Japanese is rusty). This humorous ad for them really doesn't need much in the way of translation, but if you understand Japanese, it would be neat if you would tell us what it says. -via Daily of the Day

Patricia Hill owned 104 bottles of valuable whiskey that came with the mansion she bought and converted to a historic inn in PIttsburgh. The Old Farm Pure Rye Whiskey was distilled in 1912, and was hidden under a staircase. The property had been sold several times before Hill found it during a remodeling project.   

Hill did not immediately return calls for comment. [Police chief] Pritts said that Hill put the whiskey bottles in the basement while the main floors were being renovated. John Saunders, 62, was a caretaker who lived in the basement and was expected to safeguard the booze.

"You know, to watch over them and keep them secure. I guess that was a mistake," Pritts said.

Hill discovered that 52 of the bottles had been emptied in March 2012, and reported it to police. All four cases of whiskey had been emptied within about a year, Pitts said.

Saunders denied that he consumed the vintage alcohol, but police tested the empty bottles to see if they matched Saunders' DNA. After seven months of testing, police confirmed that Saunders' DNA was found on the bottles, and charged him with felony theft and receiving stolen property, Pritts said.

The whiskey was valued at $102,400, but it is doubtful that restitution will be made. Saunders' attorney told the court that Saunders is waiting for a liver transplant. Link -via Uproxx

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YouTube member hinamitetu builds robots that do gymnastics. Here you see Gymnast Robot #16 perform a high bar routine and then dismount with a quadruple backflip -and land perfectly. They don't always work this well, as you can see in his blooper video.

The following is an article from The Annals of Improbable Research.

by Timothy C. Marzullo, Neuroscience Program, University of Michigan, Ann Arbor
Edward G. Rantze, Red Antze, Inc., Cumming, Georgia
Gregory J. Gage, Biomedical Engineering, University of Michigan, Ann Arbor

We here report for the first time, to the best of our knowledge, rat motor cortex neurons predicting the behavior of the American stock market. We implanted the motor cortex of the brains of rats with silicon electrodes. Using the correlation technique, we monitored the activity of neurons in our rats while simultaneously tracking the activity of stocks in the U.S. stock market.

Background: Hedge Funds
Hedge funds burgeoned in the early 1990's as a popular alternative to the conventional, and
more regulated, mutual funds. Hedge funds have often used alternative methods, such as
various human social factors, to predict future performance of the stock market. However, we here propose an alternative alternative method.

Methods: Correlation Analysis
For nine days, neural activity in the form of firing rates (which are the number of electrical discharges per second) from recorded neurons (n=94) of three rats were averaged each day as the rats learned to use a brain-machine interface¹ to obtain food pellets.

Mean firing rate data per day were stored using custom software (MATLAB, Mathworks Inc., Natick, MA), along with the closing stock prices for the same day for all corporations listed on NASDAQ, the New York Stock Exchange, and the American Stock Exchange (n=4195). Correlation coefficients were obtained using the corrcoef function of MATLAB, and only stocks that had significant coefficients (p <0.05, t-test) were labeled “responding” and further analyzed. See Figure 1 for a depiction of the behavioral apparatus.

Figure 1: Behavioral apparatus: rat trained on a brain-machine interface task while stocks simultaneously tracked.

Methods: Stock Market Prediction

All my life I've heard jokes about eastern Kentucky communities that were wedged between mountains and got so little sunshine that folks put mirrors on the mountains to reflect light into the valleys. Now the Norwegian town of Rjukan is actually doing just that! Rjukan is situated between two tall mountains, which limit the hours of sunlight. Between September and March, the town is in constant shadow. But now huge mirrors, carried in by helicopter, will be installed to reflect sunlight onto the town square.

Three mirrors with a total surface area of about 538 square feet will sit at an angle to redirect winter sun down into the town, lighting up over 2150 square feet of concentrated space in the town square. A similar idea exists in the Italian village of Viganella, which has used brushed steel to reflect light since 2006.

A computer located in Rjukan's main town hall office will operate the solar-powered system, which continually monitors the movement of the sun and calculates the optimal positioning of the German-made mirrors to keep the square—which the city plans to turn into a skating rink—bathed in sunlight. The project will set the Norwegians back 5 million kroner (about $835,000), but 80 percent of the funds will come privately and the system will run primariy on solar and wind power.

If it works, residents of Rjukan will have to go out on the ice to get some sunshine! Link 

A woman in Whitefield, Greater Manchester, UK, rode up to a McDonalds drive-through on a horse. The drive-through clerk refused to serve her, citing company policy. That apparently did not sit well with the woman, because she then walked inside the outlet …still on horseback! The horse pooped on the floor, the police were called, and she was issued a ticket.

A spokesman for Whitefield police said on their Facebook page: “The sight and smell of this caused obvious distress and upset to customers trying to eat, as well as staff members.

“Officers arrived at the location and woman was issued a fixed penalty notice for causing alarm and distress to other customers and staff.”

It may be an inconvenience, but when I decide to go inside a restaurant instead of using the drive-through, I usually leave my car outside. Link -via Arbroath

(Image credit: Flickr user Cindy Cornett Seigle)