Claude-assisted work extends unconditional imaginary quadratic class-number lists to 2000

Kimura reports exactly 16,453,493 imaginary quadratic fields with class number at most 2000; the largest absolute field discriminant on the list is 1,062,350,083. The classification combines an explicit zero-gap bound and discriminant bound with a sieve and previously published class-group tables.

Sources for this record

What was already known

The paper says the previously known unconditional complete list reached class number 100. Broader counts or lists up to class numbers 1000 and 1999 had relied on the generalized Riemann hypothesis. OpenAI's earlier zero-free result supplied an unquantified analytic starting point; Banks independently obtained a different explicit constant without a formal proof.

AI involvement AI-centered

Kimura says Claude Opus 5.5, under his direction, developed the explicit argument and lower bound, produced the Lean files and numerical certificates, and implemented the sieve and comparison scripts. Kimura chose the problem, the strategy, the class-number target, and the checks, worked through the proofs, and assumes responsibility. An earlier OpenAI model supplied the zero-free theorem and some upstream formalization.

Kimura credits Claude with the explicit zero-gap argument, lower bound, Lean files, certificates and sieve program. Kimura chose the class-number target and strategy, checked the proof and comparisons, and used a separate earlier OpenAI zero-free result as an input.

Importance Notable

If the computational components are correct, this extends unconditional complete classification from class number 100 to 2000 and removes a conditional assumption from several previously published ranges.

Limitations

The reported Lean and independent-kernel checks cover the explicit zero-gap and discriminant-bound theorems, not the final 16,453,493-field classification. That list also relies on an unformalized sieve program, earlier class-group tables, and extraction code. The author reports independent comparisons and spot checks, but the complete computation has not been reproduced in this review. The analytic starting point derives from an earlier OpenAI manuscript, and the author selected the target and method.

Technical verification Partial

The source reports Lean-kernel and independent nanoda checks of the explicit zero-gap and discriminant-bound theorems. These are prerequisites for the classification; the final sieve program and use of prior class-group tables are not formally verified. The author reports spot checks and comparisons, not a full independent reproduction of the final list.

Formal checking

The author reports Lean-kernel and independent nanoda checks of Theorems 1 and 10 only. These analytic bounds are prerequisites, not a formal check of the final list.

Checker
Lean kernel and nanoda, as reported by Iwao Kimura
Scope
Theorem 1 explicit zero-gap bound and Theorem 10 class-number discriminant bound; excludes sieve and table enumeration
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Full

Kimura explains the explicit-bound argument, the sieve's mathematical basis and how earlier tables enter the classification, and states that he worked through the proofs. This supports understanding of the scoped classification method, without certifying its full computation.

Correction and publication history

2026-10-18 · publication

Primary Theorem 2, prior unconditional list and GRH-conditional comparison, detailed Section 8 attribution, and distinction between formal analytic checks and unformalized final sieve reviewed; non-notifying local inclusion.

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