For the more precise numerical value see https://eikonal.wordpress.com/2010/03/09/eulers-constant-euler-mascheroni-constant-gamma/.
- , where . (source: )
- , where and . (source: )
-  “The Functions of Mathematical Physics” by Harry Hochstadt
-  “Topics in Special Functions” by G. D. Anderson, M. K. Vamanamurthy, M. Vuorinen – http://arxiv.org/abs/0712.3856