Stirling's approximation

Gives an asymptotic estimate of n! for large n, using a square root and an exponential term. It is used in combinatorics, statistical mechanics and asymptotic analysis when exact factorials are unwieldy.

n! \sim \sqrt{2\pi n}\left(\frac{n}{e}\right)^n

What the symbols mean

a positive integer (large n for the approximation to be accurate)
Euler's number, the base of the natural logarithm (approximately 2.71828)
the ratio of a circle's circumference to its diameter

About this formula

  • FieldMathematics
  • TopicFactorials and asymptotic analysis
  • LevelUniversity
  • Also calledStirling's formula, factorial approximation, approximation for factorials, n factorial asymptotic, Stirling approximation for large factorials, asymptotic formula for factorial
  • SourceWikidata Q470877

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