E (mathematical constant)
is a number. It is the base of natural logarithm and is about 2.71828. It is an important mathematical constant. The number  is occasionally called Euler's number after the Swiss mathematician Leonhard Euler, or Napier's constant in honor of the Scottish mathematician John Napier who introduced logarithms. It is equally important in mathematics as π and i.  is an irrational number, and Euler himself gave the first 23 digits of .