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.)

It is assumed that the pennies in reference are all legitimately
minted coins.

But as the problem does not stipulate that the pennies need all be the same diameter (i.e., of the same period of currency), the answer can be the small number of eight coins: six 41mm 1797 British Cartwheel pennies and two 20mm British modern day pennies. The eight pennies could be placed flat out so that each one touches three and only three other pennies.

Stipulating that each penny is identical in diameter, the answer is sixteen.

Posted by Dej Mar on 2012-10-12 20:10:16