In mathematics, the symbol e represents a natural constant, a value similar to π, and they are all irrational numbers.

And the formula for e to wait is

e= 1+ 1/( 1！ )+ 1/(2! )+ 1/(3! )+ 1/(4! )+...+ 1/(n！ )+... (the result of adding infinitely many items)

Where n! = 1*2*3*4*...*(n- 1)*n。