MathDB

A metro network with

n \ge 2

stations, where each station is connected to each of the others by a one-way line, is said to be dispersed i f there are two stations

A

and

B

such that it is not possible to go from

A

B

through is from the network. If a network is dispersed, but it is possible to choose a station

A

and reverse the direction of all lines to and from

A

so that the new network is no longer dispersed, the network is said to be correctable. Indicates all integers

n

for which there is a network with

n

stations, dispersed and not correctable.

Problem Statement