Euler, Leonhard (1736). "Theorematum quorundam ad numeros primos spectantium demonstratio" [Proof of certain theorems relating to prime numbers]. Commentarii Academiae Scientiarum Imperialis Petropolitanae (Memoirs of the Imperial Academy of Sciences in St. Petersburg) (in Latin). 8: 141–146.
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Hensel, Kurt (1913). Zahlentheorie [Number Theory] (in German). Berlin and Leipzig, Germany: G. J. Göschen. p. 103.