First studied by Leonhard Euler, it's called Euler's Number or the base of the natural logarithm and it has a value of about 2.71828, but it goes on forever and it never repeats itself. You'll often see it defined this way:

	e=	lim	(1+X)1/X
		X->0

     Another way of calculating e is as follows:

     1/0! + 1/1! + 1/2! + 1/3! + 1/4! + 1/5! + 1/6! + ...

     e^x can be found using a similar method:

     x⁰/0! + x¹/1! + x²/2! + x³/3! + x⁴/4! + x⁵/5! + x⁶/6! + ...

     An equation known as Euler's Equation states that:

     e^ix = cos(x) + i*sin(x) (proof)

What's It Good For?

ex	Calculating the Trig Functions
	Calculating xi
	Calculating ln(i)

More Resources

e Explained By Dr. Math