E is an irrational number and a transcendental number, which was first put forward by leonhard euler in 1727. He plays an extremely important role in advanced mathematics.

e= 1+ 1/ 1！ + 1/2! + 1/3! +....+ 1/(n- 1)！ + .....

It is a symbol, not produced by definition.

Of course, when n tends to infinity, the limit of (1+ 1/n) n is equal to e 。