## Combination

The number of ways of picking unordered outcomes from possibilities. Also known as the Binomial Coefficient or Choice Number and read  choose .''

where is a Factorial.

Conway, J. H. and Guy, R. K. Choice Numbers.'' In The Book of Numbers. New York: Springer-Verlag, pp. 67-68, 1996.
Ruskey, F. Information on Combinations of a Set.'' http://sue.csc.uvic.ca/~cos/inf/comb/CombinationsInfo.html.