Various facts and figures about Venn diagrams by Frank Ruskey.

A hypertext by A. Betten, H. Fripertinger and A. Kerber.

Combinatorics section of the Front for the Mathematics ArXiv.

Searchable index of problems, links and methodology.

Subfields in the AMS MSC 2000 classification 05.

A catalogue of different types with applications to packing spheres by Neil Sloane and Gabriele Nebe.

Combinatorial objects such as graphs, designs and geometries collected by Gordon Royle.

Brendan McKay's collection of miscellaneous tables in graph6 or sparse6 format.

MathWorld article with basic definitions and links.

Lecture notes by Herbert S. Wilf on generating combinatorial objects and Maple.

Searchable database of structures with specifications and counts.

A note on Catalan numbers by Ivan Galkin.

With Applications in Computer Science by Stasys Jukna.

Theory of chord structures to create music through algorithms by Vladimir Ladma.

Introduction to generating functions with interactive java applets by Alexander Bogomolny.

An introduction to partially ordered sets, Dilworth's theorem, lattices and combinatorial geometries.

An expanding web text by Joe Fields.

Computer code for research algorithms in operational research and combinatorial optimization.

Iwan Jensen counts polyominoes (aka lattice animals), paths, and various related quantities.

Select a type together with specific parameter values and COS will return a list of all such combinatorial objects.

Maintained by Bill Chen.

An unsolved combinatorial problem by Frans Faase.

Comprehensive catalog of websites relating to Combinatorics.

In the Mathematics Archive at UTK.