Solitary Number
A number which does not have any Friends. Solitary numbers include all Primes andPowers of Primes. More generally, numbers for which 
are solitary, where 
is theGreatest Common Divisor of 
and 
and 
is the Divisor Function. The first few solitarynumbers are 1, 2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 19, 21, ... (Sloane's A014567).
References
Anderson, C. W. and Hickerson, D. Problem 6020. ``Friendly Integers.'' Amer. Math. Monthly 84, 65-66, 1977. Sloane, N. J. A. Sequence A014567in ``The On-Line Version of the Encyclopedia of Integer Sequences.''http://www.research.att.com/~njas/sequences/eisonline.html.
- Bipartite Graph
- Biplanar Double Point
- Bipolar Coordinates
- Bipolar Cylindrical Coordinates
- Biprism
- Bipyramid
- Biquadratefree
- Biquadratic Equation
- Biquadratic Number
- Biquadratic Reciprocity Theorem
- Biquaternion
- Birational Transformation
- Birch Conjecture
- Birch-Swinnerton-Dyer Conjecture
- Birkhoff's Ergodic Theorem
- Birotunda
- Birthday Attack
- Birthday Problem
- Bisected Perimeter Point
- Bisection Procedure
- Bisector
- Bishop's Inequality
- Bishops Problem
- Bislit Cube
- Bispherical Coordinates