Midy's Theorem
If the period of a Repeating Decimal for 
has an Even number of digits, the sum of the two halves is a string of 9s,where 
is Prime and is a Reduced Fraction.
References
Rademacher, H. and Toeplitz, O. The Enjoyment of Mathematics: Selections from Mathematics for the Amateur. Princeton, NJ: Princeton University Press, pp. 158-160, 1957.
- Parabolic Cyclide
- Parabolic Cylinder
- Parabolic Cylinder Function
- Parabolic Cylindrical Coordinates
- Parabolic Fixed Point
- Parabolic Geometry
- Parabolic Horn Cyclide
- Parabolic Partial Differential Equation
- Parabolic Point
- Parabolic Ring Cyclide
- Parabolic Rotation
- Parabolic Segment
- Parabolic Spindle Cyclide
- Parabolic Spiral
- Parabolic Umbilic Catastrophe
- Paraboloid
- Paraboloidal Coordinates
- Paraboloid Geodesic
- Paracompact Space
- Paracycle
- Paradox
- Paradromic Rings
- Paragyrate Diminished Rhombicosidodecahedron
- Parallel
- Parallel Axiom