What is the minimum number of pennies that can be placed upon a table so that each penny touches three, and only three, others?

(All the pennies must lie flat on the table.)

(In reply to Isn't this kind of easy? by sargon)

That solution, with 4 pennies arranged in a square, has each penny touching only two other pennies. The diagonally opposite pennies are not touching.

Posted by Charlie on 2003-12-18 08:13:25