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  1. Carl Størmer: Sur l'application de la théorie des nombres entiers complexes à la solution en nombres rationnels ..........., Archiv for Math. og Naturv. 3 (1896) pp. 3-95.
  2. D.H.Lehmer: On arccotangent relations for PI, Amer. Math. Monthly 45 (1938), pp.657-664.
  3. John Todd: A problem on arc tangent relations, Amer. Math. Monthly 56 (1949), pp.517-528.
  4. Michael Wetherfield: The enhancement of Machin's formula by Todd's process, Math. Gaz. 80 (July 1996) pp. 333-344.
  5. Hwang Chien-lih: More Machin-type identities, Math. Gaz. 81 (March 1997) pp. 120-121.
  6. Ian Tweddle: John Machin and Robert Simson on Inverse-tangent Series for PI, Archive for History of Exact Sciences 42, No.1 (March 1991) pp.1-14.
  7. Amrik Singh Nimbran, "On the derivation of Machin-like Arctangent Identities for computing Pi", The Mathematics Student, Vol.. 79, Nos. 1 - 4, (2010), 171-186.
  8. The "Euler Archive":