MathDB
Problems
Contests
National and Regional Contests
Netherlands Contests
Dutch Mathematical Olympiad
2019 Dutch Mathematical Olympiad
2
2
Part of
2019 Dutch Mathematical Olympiad
Problems
(1)
n guests at a party, any 2 guests are either friends or not friends
Source: Dutch NMO 2019 p2
1/9/2020
There are
n
n
n
guests at a party. Any two guests are either friends or not friends. Every guest is friends with exactly four of the other guests. Whenever a guest is not friends with two other guests, those two other guests cannot be friends with each other either. What are the possible values of
n
n
n
?
combinatorics