When Mr. Mathwiz visited the IoK&L* he was surrounded by 20 or 21 male inhabitants, who formed a perfect circle and then each said a single word (either "Knight" or "Liar") about the man on his right.
The wiz then evaluated correctly the exact numbers of liars and the truth-tellers.
What were those numbers?
*IoK&L, is an imaginary island, inhabitated by Liars and by Truth-Tellers a.k.a. Knights.