The Primer and Twin Primer are physical ticker machines that display the next prime number with each button press. They were created by artist Karl Lautman who said,
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.