I have a number of coins. I throw them all, count how many heads and how many tails and multiply those two numbers together. I calculate what the expected (average) answer should be and discover it is exactly three times the number of coins. How many coins do I have?

(For instance if there were three coins, there are eight possibilities:

HHH TTT HHT HTH THH TTH THT HTT

The first two result in 3 x 0 = 0, and the other six result in 2 x 1 = 2, so the average answer is 1.5)