Pólya Enumeration Theorem
A very general theorem which allows the number of discrete combinatorial objects of a given type to be enumerated (counted) asa function of their ``order.'' The most common application is in the counting of the number of Graphs of 
nodes, Trees and Rooted Trees with branches, Groupsof order , etc. The theorem is an extension of Burnside's Lemma and is sometimes also called thePólya-Burnside Lemma.
References
Harary, F. ``The Number of Linear, Directed, Rooted, and Connected Graphs.'' Trans. Amer. Math. Soc. 78, 445-463, 1955. Pólya, G. ``Kombinatorische Anzahlbestimmungen für Gruppen, Graphen, und chemische Verbindungen.'' Acta Math. 68, 145-254, 1937.
- Pseudorandom Number
- Pseudorhombicuboctahedron
- Pseudoscalar
- Pseudosmarandache Function
- Pseudosphere
- Pseudosquare
- Pseudotensor
- Pseudovector
- Psi Function
- p-Signature
- PSLQ Algorithm
- PSOS Algorithm
- P-Symbol
- Ptolemy Inequality
- Ptolemy's Theorem
- Public-Key Cryptography
- Puiseaux's Theorem
- Pullback Map
- Pulse Function
- Purser's Theorem
- Pursuit Curve
- Push
- Puzzle
- P-Value
- Pyramid