Before you start

This page asks your browser to do arithmetic. If you press start, it counts prime numbers in a stretch of whole numbers nobody has checked yet, and sends back how many it found. That is the whole of it.

Nothing is installed, and nothing runs until you press start.

It uses processor time while it is running, so a laptop or phone will run warmer and use more battery. Close the tab and it stops at once.

There is no account, no email and no sign-up.

It stores three small things in this browser, using local storage rather than cookies: a random name it makes up for itself, whether you had scanning switched on, and the fact that you read this notice. They stay on your machine. Clearing this site's data removes all three.

No cookies, no analytics, no trackers, no advertising, and nothing loaded from anybody else's server.

Nothing is uploaded except counts.

The full detail is in the privacy notice and the terms. If any of it does not suit you, please leave now.

Prime Scan

Your browser checks a block of numbers nobody has looked at.

Primes thin out as they get bigger and they seem to do it very evenly, no bunching, no gaps where a pile should be. Nobody knows why, and nobody can prove it stays true forever. So we look: your browser takes a stretch nobody has checked, finds the primes in it, and sees whether they sit as evenly as they should. If they ever don't, that is worth a very long look.

your ID—

block at—

blocks done · 5,000,000 numbers each 0

primes found0

statusidle

everyone so far — people · — blocks · — primes
reaching — · — numbers checked · — double-checked