Lowercase e, as a mathematical constant, is the base of natural logarithmic function. Sometimes it is called Euler number, named after the Swiss mathematician Euler. E = 2.7 1828 182 ... is one of the two commonly used limits in calculus. It is one of the most important constants in mathematics, just like pi and imaginary units I and E.

The origin of e

1690, Leibniz first mentioned the constant e in his letter. The constant E mentioned for the first time in this paper is a table in the appendix of John Napier's logarithmic works published in 16 18. But it didn't record this constant, only a list of natural logarithms based on it, which is generally believed to be made by William Oughtred. It was Jacob Bernoulli who first thought that e was a constant. Euler also heard of this constant, so at the age of 27, E was "guaranteed" to calculus by publishing a paper.