Casting Out Nines
An elementary check of a Multiplication which makes use of the Congruence 
(mod 9) for 
. From this Congruence, a Multiplication 
must give
so
must be 
(mod 9). Casting out nines is sometimes also called ``the Hindu Check.''
References
Conway, J. H. and Guy, R. K. The Book of Numbers. New York: Springer-Verlag, pp. 28-29, 1996.
- Segner's Recurrence Formula
- Segre's Theorem
- Seiberg-Witten Equations
- Seiberg-Witten Invariants
- Seidel-Entringer-Arnold Triangle
- Seifert Circle
- Seifert Conjecture
- Seifert Form
- Seifert Matrix
- Seifert's Spherical Spiral
- Seifert Surface
- Self-Adjoint Matrix
- Self-Adjoint Operator
- Self-Avoiding Walk
- Self-Conjugate Subgroup
- Self-Descriptive Number
- Self-Homologous Point
- Self Number
- Self-Reciprocating Property
- Self-Recursion
- Selfridge-Hurwitz Residue
- Selfridge's Conjecture
- Self-Similarity
- Self-Transversality Theorem
- Selmer Group