Invented by ‘David’ on David’s Site, he points out that the number of resistors rises rapidly with the number of wires as: (number of wires) * (number of wires – 1)/2

So one resistor with two wires, three with three, six with four wires and 45 with 10, etc.

Not only this, but David has written the technique out clearly on his blog alongside nice clear diagrams.

According to Hackaday, David has got the technique running on a ATMega32.