Primer and Twin Primer are kinetic sculptures that generate prime numbers. Just push the button, and they count up to the next one. Prime numbers are the only numbers they're ever going to display. Even if they count up to 999,999 (or 9,999,999 for Twin Primers), they'll just roll over and stop at 2, the first prime number. Then they start all over again. You can see a detailed video I made about Primer here (I made it for a Kickstarter campaign in 2013) and one made by the Numberphile blog here.
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.
Both Primers are a great addition to any office or cubicle, and make a perfect gift for the mathematician or engineer in your life, or anyone who just likes pushing a button and seeing something happen.
They each cost $160, 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 make your selection below and click "Buy Now." 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
Twin Primer dimensions: 4"W x 4"D (base) x 4.75"H
PS - If you're too cheap to actually buy one of these, here's a free Android app that simulates them, created by Yoah Bar-David.