Leonhard Euler produced a large share of his roughly 850 works after going blind — but the exact fraction is unsettled, with two Tier-2 sources giving conflicting figures

Leonhard Euler, who lost his remaining sight around age sixty, continued to produce mathematics at scale through memory and dictation to trained assistants. That he produced a large share of his roughly 850 total works after going blind is corroborated by two independent academic sources — but they disagree on the size of that share, so the exact figure is not settled:

• Allyn Jackson, Notices of the AMS (2002): "having produced around 850 works. Amazingly, half of his output came after his blindness." → half.
• Mele & Sicignano (2021), drawing on Calinger's Leonhard Euler: Mathematical Genius in the Enlightenment (Princeton UP, 2019): "he produced almost a third of his results in the first seven years after completely losing his sight at the age of sixty." → ≈ a third, in seven years.

These are not the same claim: "half of all output, over the remaining ~17 years" and "almost a third, in the first seven years" measure different windows and could both be true, or neither exactly. Both sources are Tier 2. Because this is a quantitative claim (sourcing floor Tier 1–2) resting on a source conflict, the note keeps status: seedling and carries [unverified-quant]; the exact fraction and count need a primary source (Euler's Opera Omnia catalogue / the Eneström index, or Calinger directly). Verification is routed at question-verify-euler-post-blindness-output-fraction.

This upgrades the previously unsourced Euler "further lead" folded into claim-blind-mathematicians-independently-reinvented-private-notation, where Euler stands as the "memory / dictation" case alongside Saunderson's touch and Pontryagin's speech. (Note: that anchor note gives Euler's age at sight loss as "around 27," which the better-sourced figure here — completely blind "at the age of sixty" — appears to correct; the ~27 likely refers to loss in one eye.)

2026-08-01 follow-up. A later capture traced the "half" figure to an 1883 Rudio lecture with no independent count behind any of its retellings, found that Euler's total-work count itself ranges 560–866 across sources, and found that the "seven years" cited in different accounts are not the same seven years. None of this resolves the fraction; see question-verify-euler-post-blindness-output-fraction for the current state.