Hyperreal Number
Hyperreal numbers are an extension of the Real Numbers to include certain classes of infinite and infinitesimal numbers. A hyperreal number 
is said to be finite Iff 
for some Integer 
. is said to be infinitesimalIff 
for all Integers .
References
Keisler, H. J. ``The Hyperreal Line.'' In Real Numbers, Generalizations of the Reals, and Theories of Continua (Ed. P. Ehrlich). Norwell, MA: Kluwer, 1994.
- Repunit
- Residual
- Residual vs. Predictor Plot
- Residue Class
- Residue (Complex Analysis)
- Residue (Congruence)
- Residue Index
- Residue Theorem (Complex Analysis)
- Residue Theorem (Group)
- Resolution
- Resolution Class
- Resolution Modulus
- Resolvable
- Resolving Tree
- Resonance Overlap
- Resonance Overlap Method
- R-Estimate
- Restricted Divisor Function
- Restricted Growth Function
- Restricted Growth String
- Resultant
- Retardance
- Reuleaux Polygon
- Reuleaux Triangle
- Reversal