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3. J. W. Wrench, Jr. & L. B. Smith, “Values of the terms of the Gregory series for arccot 5 and arccot 239 to 1120 and 1150 decimal places, respectively,” MTAC, v. 4, 1950, p. 160-161.
4. A new approximation to 𝜋. II;Ferguson, D. F.;Math. Tables Aids Comput.,1948
5. Modular equations and approximations to 𝜋 [Quart. J. Math. 45 (1914), 350–372];Ramanujan, S.,2000