The natural constant is a constant in mathematics, an infinite acyclic decimal and a transcendental number, which is about 2.7 1828, that is, the formula is IIM (1+ 1/x) x, x →

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.

The earliest known uses of the constant e are 1690 and 169 1 year, which is represented by B. In 1727, Euler began to use e to represent this constant. The first use of e in publications is Euler mechanics in 1736. Although some researchers later used the letter C, E was widely used and finally became the standard.

The reason why E is used is really unknown, but it may be because E is the first letter of the word "index". Another view is that A, B, C and D have other common usages, and E is the first available letter. Another possibility is that the letter "e" refers to the first letter of Euler's name "Euler".