8.6. First solution. Divide all the coins into two parts of 20 coins each and weigh them. Since the number of counterfeit coins is odd, one of the piles will weigh more. This means that there is no more than one counterfeit coin in it. Divide it into two piles of 10 coins and weigh them. If the scales are in balance, then all 20 weighed coins are genuine. If one of the pans outweighs, then there are 10 genuine coins on that pan, and among the other 10 coins, there is exactly one counterfeit. Divide these 10 coins into three piles of 4, 4, and 2 coins. In the third weighing, compare the two piles of 4 coins. If they balance, then all 8 coins are genuine and we have found 18 genuine coins. If one of the piles outweighs, then there are 4 genuine coins in it, the other pile contains the counterfeit coin, and the 2 set aside coins are genuine. In total, 16 genuine coins have been found.
The second solution. Divide all the coins into five equal piles, each containing 8 coins, and number them. Place the 1st and 2nd piles on one side of the scales, and the 3rd and 4th piles on the other.

Consider the first case - the scales balance. Then either there is one fake coin on each side, or all the coins being weighed are genuine. Then we will weigh the 1st and 2nd piles. If they balance, then all 16 coins are genuine. If one of the piles outweighs the other, then it contains 8 genuine coins. The third weighing will compare the 3rd and 4th piles to determine the next 8 genuine coins.

Now consider the second case - the scales do not balance. Let's assume for definiteness that the 1st and 2nd piles outweigh the others, then among them there is no more than one fake coin. The second weighing will compare the 1st and 2nd piles. If they balance, then all 16 coins are genuine. If one of the piles outweighs the other, then it contains 8 genuine coins, and the other has exactly one fake coin. Consequently, the 3rd and 4th piles contain exactly two fake coins, and the 5th pile contains 8 genuine coins. Thus, a total of 16 genuine coins have been found.