Portal:Mathematics/Featured article/2006 5
{{Portal:Mathematics/box-header|Selected article|{{FULLPAGENAME}}}} The Catalan numbers, named for the Belgian mathematician Eugène Charles Catalan, are a sequence of natural numbers that are important in combinatorial mathematics. The sequence begins: The Catalan numbers are solutions to numerous counting problems which often have a recursive flavour. In fact, one author lists over 60 different possible interpretations of these numbers. For example, the nth Catalan number is the number of full binary trees with n internal nodes, or n+1 leaves. It is also the number of ways of associating n applications of a binary operator as well as the number of ways that a convex polygon with n + 2 sides can be cut into triangles by connecting vertices with straight lines. |align=left|...Archive |align=center| |align=right|Read more...style="float: right; margin-left: 1em; background-color: transparent; " 175px width=175 style="font-size: 85%; text-align: center; " | 14 ways of triangulating a hexagon width="100%" border="0" style="clear:both; padding:0; margin:0; background:transparent;"
