e

One of the most important mathematical constants, e is the base for natural logarithms. A number's natural logarithm is the value, which when raised to the e power, equals that number. For example, the natural logarithm of 10 is 2.3025850929940456840179914546844, since e raised to the power of 2.3025850929940456840179914546844 equals 10.

No one knows the exact value of e. That's because it belongs to a class of numbers known as "irrational", numbers that cannot be expressed by a finite number of digits. A recently-computed approximation of e had over 2 million digits, still leaving an infinite number of digits to be determined.

For most purposes, a value of e accurate to 5-10 digits is sufficient. Karen's Calculator program can insert an approximate value of e into a calculation. That program lets you choose the precision of the value, ranging from one digit to the right of the decimal point, to as many as 10,000 digits to the left of the decimal point. 

The value of e, accurate to 50 digits, is: 2.71828182845904523536028747135266249775724709369996

Note: e is often called Euler's Number (because of his discovery of a way to calculate its value), or Napier's Constant (because of his early work in the field of logarithms).