where is its radius.
The ordinary sphere in three-dimensionalEuclidean space is a 2-sphere. The term derives from
the Latin "glomus" meaning "ball of string" (Whitney 1889-1891,
p. 2542).
Agboola, D.; Knol, A. L.; Gill, P. M. W.; and Loos, P.-F. "Uniform Electron Gases. III. Low-Density Gases on Three-Dimensional
Spheres." J. Chem. Phys.143, 084114, 2015. https://doi.org/10.1063/1.4929353.Whitney,
W. D. (Ed.). The Century Dictionary: An Encyclopedic Lexicon of the English
Language. New York: Century Co., p. 2542, 1889-1891.