Triangle Coefficient

The triangle coefficient is function of three variables written  and defined by

(Shore and Menzel 1968, p. 273), where  is a factorial. It arises for example in the definition of the Wigner 6j-symbol.

REFERENCES:

Messiah, A. Quantum Mechanics, Vol. 2. Amsterdam, Netherlands: North-Holland, p. 1058, 1962.

Shore, B. W. and Menzel, D. H. Principles of Atomic Spectra. New York: Wiley, 1968.