Recreational Mathematics

Here are some net resources for recreational mathematics that I've really
enjoyed, especially links to topics in tiling the plane and in number theory.

Tessellations
World of Escher
Hyperbolic Tessellations
Wallpaper Groups
John Mount's Home Page

Number Theory
- The Uselessness of Pi ...
  Data Powers of 10
  The Prime Pages
  Fun with Numbers
  Number Theory Web

Other Stuff
Archimedes' Laboratory
Recreational Mathematics
Difficult Crossings
Kids Web-Math
Scott Kim's Inversions,Games & Puzzles
Binary Arts (The Smart Toy Company)