For and and not integers,
Dougall's Formula
See also
Gamma FunctionExplore with Wolfram|Alpha
References
Erdélyi, A.; Magnus, W.; Oberhettinger, F.; and Tricomi, F. G. Higher Transcendental Functions, Vol. 1. New York: Krieger, p. 7, 1981.Referenced on Wolfram|Alpha
Dougall's FormulaCite this as:
Weisstein, Eric W. "Dougall's Formula." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DougallsFormula.html