As a mathematical constant, e is the base of natural logarithmic function, sometimes called Euler number, named after Swiss mathematician Euler; There is also a relatively rare name Napier constant to commemorate the introduction of logarithm by Scottish mathematician John Napier. E is one of the most important constants in mathematics.

Both natural constants e and pi are unique transcendental numbers, but the popularity of natural constants is much lower than that of pi, because pi is easier to satisfy in real life, while natural constants are not commonly used in daily life. The most perfect Euler formula combining e and π is also the highest embodiment of the mathematical value of transcendental number e.