    # 2.71828182845904523536028747135266249775

## Growing Outta Control

e might seem like an odd number at first, but it has a lot of special properties that makes it worth knowing about. It can be used to construct perfect arches, calculate continuous interest, and plot a trip where the distance you have traveled is always the same as your speed, which is always the same as your acceleration. It creates the ultimate exponential, growing without bound. ## e's Spiffy Properties

• the first mention of e occurs in 1618
• e is used to find interest that is accumulated continuously, the method commonly used by banks
• an equation involving e describes a catenary, the shape of hanging cords that are flexible but not stretchy
• the Gateway Arch in St Louis, Missouri has the shape of an upside down catenary
• e is involved in the equation for the statistical bell curve
• The sum • The area underneath 1/x from 1 to e is 1
• e is irrational, because it cannot be expressed as a fraction of whole numbers
• e is transcendental, because there is no polynomial with rational coefficients of which e is a root
• the value of ex at any point is the same as its slope at that point
• the infinite digits of e have no pattern