Witness
A witness is a number which, as a result of its number theoretic properties, guarantees either the compositeness orprimality of a number 
. Witnesses are most commonly used in connection with Fermat's Little Theorem Converse. A Pratt Certificate uses witnesses to prove primality, and Miller's Primality Test uses witnesses to provecompositeness.
- Concentrated
- Concentric
- Concentric Circles
- Conchoid
- Conchoid of de Sluze
- Conchoid of Nicomedes
- Concho-Spiral
- Concordant Form
- Concur
- Concurrent
- Concyclic
- Condition
- Conditional Convergence
- Conditional Probability
- Condition Number
- Condom Problem
- Condon-Shortley Phase
- Conductor
- Cone
- Cone Graph
- Cone Net
- Cone (Space)
- Cone-Sphere Intersection
- Confidence Interval
- Configuration