Euler’s number, the number e, is a mathematical constant approximately equal to 2.71828. You encounter the number e in mathematics almost every day because it is the base of the natural logarithm, the limit of (1 + 1/*n*)*n* as *n* approaches infinity, and an expression that arises in the study of compound interest.

## Boltzmann’s Constant

The fundamental constant of physics, the Boltzmann constant, is one of the seven "defining constants" that have been given exact definitions.