Smallest unsolved instance of the Hadamard conjecture
23a
Upper bound, last-listed row
| $\infty$ | Trivial | No finite upper bound is known; conjecturally sharp (Hadamard conjecture). |tracked since 2026-07-24 — no movement seen yet
Lower bound, last-listed row
| $668$ | [CP2024] | All orders $n<668$ with $n\equiv 0\pmod4$ are known to admit Hadamard matrices; the smallest currently unresolved order is $668$. |tracked since 2026-07-24 — no movement seen yet
Cite this rowBounds Ledger — Smallest unsolved instance of the Hadamard conjecture (23a)
upper bound: $\infty$ (tracked since 2026-07-24 — no movement seen yet)
lower bound: $668$ (tracked since 2026-07-24 — no movement seen yet)
Mirrored from teorth/optimizationproblems@2c1968c. These are the last-listed rows of that constant's bounds table — a listing position, not a statement that this bound is the strongest or most recent. A snapshot at that sha, not a live read.
https://u00dxk2.github.io/bounds-ledger/c/23a.html