Apocalypse Number
A number having 666 Digits (where 666 is the Beast Number) is called an apocalypse number. TheFibonacci Number 
is an apocalypse number.
References
Pickover, C. A. Keys to Infinity. New York: Wiley, pp. 97-102, 1995.
- Circle Tangents
- Circuit
- Circuit Rank
- Circulant Determinant
- Circulant Graph
- Circulant Matrix
- Circular Cylindrical Coordinates
- Circular Functions
- Circular Permutation
- Circumcenter
- Circumcircle
- Circumference
- Circuminscribed
- Circumradius
- Circumscribed
- Circumsphere
- Cis
- Cissoid
- Cissoid of Diocles
- Cissoid of Diocles Caustic
- Cissoid of Diocles Inverse Curve
- Cissoid of Diocles Pedal Curve
- Clairaut's Differential Equation
- Clarity
- Clark's Triangle