52

Part of 1982 IMO Longlists

Problems(1)

For each k, there are exactly k numbers between the two k

Source: IMO LongList 1982 - P52

2n

natural numbers

1, 1, 2, 2, 3, 3, \ldots, n - 1, n - 1, n, n.

n

for which these numbers can be arranged in a row such that for each

k \leq n

, there are exactly

k

numbers between the two numbers

k

invariantmodular arithmeticcombinatorics proposedcombinatorics