Euler-Mascheroni Constant Definition

A constant, denoted γ and recurring in analysis and number theory , that is defined as the limiting difference between the harmonic series and the natural logarithm and has the approximate value 0.57721566.

Wiktionary

Origin of Euler-Mascheroni Constant

Named after mathematicians Leonhard Euler (1707—1783) and Lorenzo Mascheroni (1750—1800). The origin of the notation γ is unclear: it may have been first used by either Euler or Mascheroni. It possibly reflects the constant's connection to the gamma function .

From Wiktionary