Question 1
Among a group of $451$ persons, every pair of persons together know exactly one other person (knowing is mutual). Denote by $n$ the difference between the number of persons known by a member of the group who knows the largest number of persons among the group, and the number of persons known by another member who knows the smallest number of persons among the group. Find the maximum possible value of $n$ and all other possible value(s) of $n$.