Ulam Spiral
Primes · 30 levels
Sweep the spiral sky until only the primes shine.
How to play
- The numbers wind out on a square spiral. Pick a brush, then touch any multiple of it.
- Every multiple of the brush number (but not the brush number itself) fades to dust: brush 3 clears 6, 9, 12…
- Clear every non-prime within the stroke limit. Only the primes stay lit, and their diagonal lines glow.
Every non-prime up to N has a factor no bigger than √N. Up to 100 you only need 2, 3, 5 and 7. In a window of big numbers, check each brush: does it clear anything the smaller ones miss?
Teeter, Tint and Echo Heist are free starters. Other games unlock through earned game choices or permanent packs. Your progress stays in the browser; optional sign-in saves it to your website account.