1. The problem statement, all variables and given/known data There are N villages which have to be connected using one-way roads in a manner that for every two villages there exists at least one route to travel from one to another. How many different solutions are there? 2. Relevant equations This fits pretty well not only into combinatorics but also in a graph theory. 3. The attempt at a solution For N=2 there is only 1 trivial solution. For N=3 there seems to be 15 solutions, but it's done by writing out the combinations and does not lead to general solution.