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Related to Ramanujan's fast converging series expansion for pi.
S. Ramanujan, 'Modular equations and approximations to\pi', Quart. J. Math. 45 (1914), 350-372.
Table of n, a(n) for n=11..115.
Wolfram Mathworld, Pi Formulas
Sequence in context: A104311 A200818 A021980 * A011175 A109534 A276163
Adjacent sequences: A169621 A169622 A169623 * A169625 A169626 A169627
Mark A. Thomas, Dec 03 2009