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3

Part of 1997 Finnish National High School Mathematics Competition

Problems(1)

Knights at a round table

Source: Finnish Mathematics Competition 1997, Final Round, Problem 3

11/14/2011
1212 knights are sitting at a round table. Every knight is an enemy with two of the adjacent knights but with none of the others. 55 knights are to be chosen to save the princess, with no enemies in the group. How many ways are there for the choice?
combinatorics unsolvedcombinatorics