Primer is a kinetic sculpture that generates prime numbers. Just push the button, and it counts up to the next one. Prime numbers are the only numbers it's ever going to display. Even if it counts up to 999,999, it'll just roll over and stop at 2, the first prime number. Then it starts all over again. You can see a video about Primer made by the Numberphile blog here. Here's how I make them. And here's the 2013 Kickstarter video.
I get the counters that I use on eBay, so they're generally (though not always) used. This means any particular counter may or may not be like new, but, rest assured, I'll never use one that's a mess or that you wouldn't be proud to show (or give) to your friends.
Primer is a great addition to any office or cubicle, and makes a perfect gift for the mathematician or engineer in your life, or anyone who just likes pushing a button and seeing something happen.
Primer costs $170, which includes tax and US ground shipping (international shipping via express mail is $60 extra, which does not include import duties (£50 in the UK, e.g.)). If you'd like to order one (and I strongly urge you to do so), just click "Buy Now" below. Thanks!
Shipping to the UK? Because of duty and bulk shipping, you'll get a better deal buying your Primer from Maths Gear (plus they carry lots of other cool maths-related stuff).
Primer dimensions: 4"W x 5.5"D (base) x 6.5"H
PS - If you're too cheap to actually buy one of these, here's a free Android app that simulates one, created by Yoah Bar-David.
PPS - Lost the instructions? Here's a copy.