Least universal exponential base for Euclidean kissing numbers

What is the least α such that the Euclidean kissing number τₙ≤αⁿ in every positive dimension with no prefactor? The stated target is α=√6, with τ₂=6 attaining the base and the maximum τₙ attained in every dimension.

Why it matters and what counts as progress

Why it matters: It asks for an exact universal bound valid at all dimensions, a different optimization from prefactor-bearing asymptotic estimates.

What counts as progress: Prove the all-dimensional no-prefactor bound and a dimension attaining the base. An asymptotic bound with a prefactor addresses a different optimization.

How the problem developed

  1. 4 Oct 2017 · Open question [1]

    Sébastien Palcoux Asked for the smallest α such that every Euclidean kissing number satisfies τₙ≤αⁿ, and whether α=√6.

  2. 5 Sept 2026 · Formalized proof [2][3]

    GPT-6 Astra, prompted by Sébastien Palcoux Registered a Lean-verified proof that τₙ≤(√6)ⁿ for all positive n and that √6 is the least universal exponential base without a prefactor.

AI contribution

The optimal universal exponential base for Euclidean kissing numbers

Sébastien Palcoux

For every positive dimension n, the Euclidean kissing number τₙ is an attained maximum and satisfies τₙ≤(√6)ⁿ. A planar hexagon gives τ₂=6, so √6 is the least base in a bound τₙ≤αⁿ valid in every dimension without a prefactor.

AI involvementAI-led
ImportanceNotable
Human understandingFew
Reported

Sources

  1. 2017 universal-base question
  2. Sébastien Palcoux, Proof and conditional Lean certificate for the universal sqrt(6) kissing-number bound
  3. Sébastien Palcoux, Palomar registration and submission record
  4. Universal kissing-number submission
  5. Pinned theorem and AI disclosure
  6. Pinned formalization and audit scope
Website timeline

Publication dates and editorial changes.