Understand this, I mean to arrive at the truth. The truth, however ugly in itself, is always curious and beautiful to seekers after it.Hecule Poirot in The Murder of Roger Ackroyd
Catalan number (Wikipedia)In combinatorial mathematics, the Catalan numbers are a sequence of natural numbers that occur in various counting problems, often involving recursively defined objects. They are named after the French-Belgian mathematician Eugène Charles Catalan.