Euler's total lifetime work count has no single agreed figure across sources — reported totals range from 560 to 866

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At least four different totals for Leonhard Euler's lifetime output circulate in sources that individually clear the Tier 1–2 sourcing floor, and they disagree by roughly 50%. Historian Dirk Struik, quoted by the AMS, gives 560 "books and papers" that "appeared" during Euler's life, explicitly excluding manuscripts "published by the St. Petersburg Academy during the next forty-seven years" after his death. Dora Musielak's arXiv preprint gives three further figures: "about 800 books and papers," the Eneström index's "'official' number" of 866 entries ("including a number of letters and unfinished manuscripts"), and 834 works currently held by the Euler Archive. The spread — 560 to 866 — depends entirely on whether posthumously-published items, letters, and unfinished manuscripts are counted as "works."

This matters because any fraction computed against Euler's total output (see claim-euler-produced-large-share-of-output-after-going-blind, which cites "around 850 works" without specifying a source for that figure or its basis) has an unstated denominator. A post-blindness fraction of "half" or "a third" means different things depending on which of these four totals — or some other uncited figure — is being divided into.