complement
and 
. If such a complement exists, then every element can be uniquely written as hk. But a complement need not exist, nor be unique if one does.
- radius of gyration
- radius vector
- raise
- Ramanujan, Srinivasa
- Ramsey, Frank
- Ramsey Theory
- random
- random error
- random graph
- randomization
- randomize
- randomized blocks
- random numbers
- random sample
- random variable
- random vector
- random walk
- range
- range
- range
- rank
- rank
- rank correlation coefficient
- rank-nullity theorem
- rate of change