3

Part of 2000 China Second Round Olympiad

Problems(1)

How many times do people contact with others

Source: 2000 China Second Round Olympiad P3

n

people, and given that any

2

of them have contacted with each other at most once. In any group of

n-2

of them, any one person of the group has contacted with other people in this group for

3^k

k

is a non-negative integer. Determine all the possible value of

n.

combinatoricsgraph theory