Binomial coefficient formula

Gives the number of ways to choose k items from a set of n items without regard to order, for integers 0 ≤ k ≤ n. It is the coefficient of the term x^k y^(n-k) in the expansion of (x+y)^n.

\binom{n}{k} = \frac{n!}{k!\,(n-k)!}

What the symbols mean

total number of items in the set (a non-negative integer)
number of items chosen (an integer with 0 \leq k \leq n)
factorial of n, the product of all positive integers up to n

About this formula

  • FieldMathematics
  • TopicCombinatorics
  • LevelHigh school
  • Also calledn choose k, choose formula, binomial coefficient, combinations formula, number of combinations, nCk
  • SourceWikidata Q209875

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