The golden section.

e is 2.718, which is approximately equal to 2.72. In 1683, when the famous Swiss mathematician Jacob Bernoulli (1654-1705) was studying continuous compound interest, he realized that the problem must be solved in the extreme way. solve. However, he only proposed one formula, thinking that the number should be between 2 and 3, and did not obtain complete data. Because at that time, there was no concept of limits.

The first mention of the constant e is in a table in the appendix to John Napier's book on logarithms published in 1618. It does not record this constant, but only a list of natural logarithms calculated from it as a base, usually attributed to William Oughtred. The first person who regarded e as a constant was Jacob Bernoulli. He tried to calculate the value of the following formula: (1 1/n) to the nth power, and found its limit when n tends to infinity.

The first known use of the constant e is from Leibniz's correspondence to Huygens in 1690 and 1691, represented by b. In 1727, Euler began to use e to represent this constant; and the first time e was used in publications was Euler's "Mechanica" in 1736. Although some researchers used the letter c to represent it in the years to come, e was more commonly used and finally became the standard.

The reason why e is used is unknown, but it may be because e is the first letter of the word "exponential". Another view is that a, b, c and d have other common uses, while e is the first available letter. However, the reason why Euler chose this letter is unlikely to be because it was the initials of his own name, Euler, because he was a very humble person who always appropriately recognized the work of others.