Pair Sum
Given an Amicable Pair 
, the quantity
is called the pair sum, where
is the Divisor Function and 
is the Restricted Divisor Function. See also Amicable Pair- Ultraspherical Differential Equation
- Ultraspherical Function
- Ultraspherical Polynomial
- Umbilic Point
- Umbral Calculus
- Umbrella
- Unambiguous
- Unbiased
- Uncia
- Uncorrelated
- Uncountable Set
- Uncountably Infinite Set
- Undecagon
- Undecidable
- Undecillion
- Undetermined Coefficients Method
- Undulating Number
- Unduloid
- Unexpected Hanging Paradox
- Unfinished Game
- Unhappy Number
- Unicursal Circuit
- Uniform Apodization Function
- Uniform Boundedness Principle
- Uniform Convergence