Let
See also Lemniscate
References
Abramowitz, M. and Stegun, C. A. (Eds.).
Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing.
New York: Dover, 1972.
Borwein, J. M. and Borwein, P. B. Pi & the AGM: A Study in Analytic Number Theory and Computational Complexity.
New York: Wiley, 1987.
Finch, S. ``Favorite Mathematical Constants.'' http://www.mathsoft.com/asolve/constant/gauss/gauss.html
Le Lionnais, F. Les nombres remarquables. Paris: Hermann, p. 37, 1983.
Todd, J. ``The Lemniscate Constant.'' Comm. ACM 18, 14-19 and 462, 1975.