In mathematics, at least four different functions are known as the pi or Pi function:

  • <math>\pi(x)\,\!</math> (pi function) &ndash; the prime-counting function
  • <math>\Pi(x)\,\!</math> (Pi function) &ndash; the gamma function when offset to coincide with the factorial
  • Rectangular function
  • <math>\pi(n)\,\!</math> &ndash; the Pisano period

It may also refer to:

  • <math>\prod_{n=1}^{\infty}</math> &ndash; the Infinite product of a sequence
  • Capital pi notation