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

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.