# “If the answer here doesn’t blow your mind, I don’t know what will.”

3Blue1Brown: The most unexpected answer to a counting puzzle and So why do colliding blocks compute pi? and How colliding blocks act like a beam of light…to compute pi. (YouTube, 5:12min and 15:15min and 14:40min)

The connection between the initial experiment and the calculation of π is surprising, and finding two different solutions in physics is even more astounding. The videos are extremely well done, and the presentation helps a lot with understanding the mathematical manipulations.

Mind. Blown.

# A three-digit number is evenly divisible by 7 if and only if…

Futility Closet: Even Sevens.

I know a lot of rules to determine divisibility, but I never knew there were any for divisibility by seven. Here’s one!

# It’s a spherical video in a mathematically triplified space with symmetry in space-time

Vihart: Peace for Triple Piano. (YouTube 3D video, 4:15min)

This has got to be one of the most amazing things done with a 3D camera I’ve ever seen. Pro tip: Watch this in fullscreen mode on your phone so you can look around by moving the entire phone, and use headphones to get the full 3D sound effect as well.

Make sure to also watch

Henry Segerman: The Making of “Peace for Triple Piano”. (YouTube video, 13:52min including a “flat” version of the above 3D video).

In this video Vi Hart and Henry Sergerman explain how the video works: how they made one grand piano and one Vi look like three, but one Henry look like only two at the same time.

(This was published back in February, but I only now realized that the RSS feed of this YouTube channel stopped working.)

# Friday Fun

OK Go: The One Moment – Official Video. (YouTube, 4:12min)

A music video that was shot in just four seconds and then slowed down to fit over four minutes of music. Here’s how they did it:

OK Go Sandbox: OK Go Sandbox – One Moment of Math. (YouTube, 4:33min) “Damian Kulash, lead singer of OK Go, discusses the immense amount of math behind their video,”The One Moment”.”

The rest of the OK Go Sandbox is worth checking out as well.

# “If you’re not great at math, here’s a primer: Prime numbers can only be divided by 1 and themselves. “

NPR: A Tenn. Man Recently Discovered The Largest Prime Number Known To Humankind. “This past week, a FedEx employee from Germantown, Tenn., made a massive discovery — and it wasn’t in any packages. John Pace found the largest prime number known to humankind. And that number goes on to more than 23 million digits.”