The Euler-Mascheroni Constant, typically written as the letter γ (a lowercase Greek gamma) is a constant found in many places in number theory and analysis. It can be defined as the limit as n goes to infinity of the sum, k equals one to n, of the quantity one over k minus the natural logarithm of k.

The value now known as γ was first published by Euler in 1735, in De Porgressionibus harmonicis observationes. Euler published his constant to five correct significant digits; he later extended it to 16 digits in 1781. To earn his place in the name of the constant, Lorenzo Mascheroni, an Italian professor of mathematics, published 32 digits in 1790, though he got the last 13 of them wrong. The current limit is ten billion digits, computed by S. Kundo in 2008. Despite knowing this number out to so many places, it is still unknown if it is irrational. Work continues to tease out its properties, as it is a key number in the mathematics underlying many systems.

γ shows up in many places in analysis, the manipulation of functions, and in number theory, the study of the behavior of numbers. As such, it is a useful constant and it has a large impact on many important questions. By computing better approximations, it becomes possible to better model systems, allowing scientists to make better predictions and engineers to build novel solutions to problems.

For instance, gamma is essential to computing the mean of the Gumbel distribution, which is used to predict future maxima and minima based on previous observations of the extrema. This allows scientists to predict the probability that an extreme event, such as a natural disaster, will occur in a given period of time.

γ is also strongly related to the "gamma function," which is a generalization of the factorial function. In fact, the Euler-Mascheroni Constant was named γ after the gamma function. With this formula, mathematicians and scientists are better able to model things ranging from cryptographic systems to physics, allowing new devices and secure transactions.

γ shows up in solutions of Bessel functions, which are used to model wave-like systems. This includes the design of waveguide antennas, the vibration of drum heads, and the conduction of heat through objects, all important problems when designing a cell phone.

Despite its long history, mathematics is full of unresolved questions. These are entities like the Euler-Mascheroni constant: things we have known about for many years, but still haven't fully analyzed. Resolving the nature of this constant could enable better solutions, but it has proven difficult to pull apart. Despite this, mathematicians have found "good enough" approximations to enable scientists and engineers to make use of gamma, and it will only get better from here.