\(s (47)\)$s(47)$ — solved

\(s(47) = 7\)$s(47)=7$. Established by chelokot’s Lean proof (2026), replayed here with its axiom receipt, of the family \(s(k^2 - 2) = k\)$s(k^2-2)=k$ that Nagamochi’s general theorem (2005) stated first; Nagamochi’s Lemma 1, on which his proof rests, is false. Lean theorem: s(n^2 - 2) = n for every integer n >= 2.

The packing

The record catalogue does not picture \(n = 47\)$n=47$: no arrangement has ever been found that beats the trivial \(\lceil\sqrt{47}\rceil = 7\)$\lceil \sqrt{47}\rceil =7$ grid, so the grid is still the best known packing. That is a statement about what has been searched, not a proof.

The lower bound

The strongest lower bound independently verified in this record is chelokot’s Lean theorem, replayed here with its axiom receipt, which applies to every \(n \ge 2\)$n\ge 2$:

Correction, 2 October 2026. Until that date the verified lower bound here was Nagamochi’s general closed form, \(s(N) \ge \min(\lceil\sqrt{N}\rceil, \sqrt{N - 2\lfloor\sqrt{N}\rfloor + 1} + 1)\)$s(N)\ge min(\lceil \sqrt{N}\rceil ,\sqrt{N-2\lfloor \sqrt{N}\rfloor +1}+1)$, which gives the same value at this \(n\)$n$ and is now recorded as a reported bound. Its published proof rests on Nagamochi’s Lemma 1, which Karakuş showed false, and chelokot’s proof does not use it (review of 2 October 2026). This register had recorded that proof as verified, its own error, logged as defect D-516.

See the Frontier corpus summary for the current aggregate count; source-reported bounds are recorded separately.

Verification Code

The programs behind this case’s verified bounds, by their evidence. The code column says how the code that ran stands to the code its producer used. VERIFIERS.md says what each program is and whose it is.