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Every odd number above one and below 330750 has a strictly smaller Syracuse iterate

Proved
syracuse_descends_below_330750

by Zexuan Liu · Sep 9, 2026 · Mathlib 0df444a (Lean v4.33.1)

collatznumber-theory

Let TTT be the Syracuse map, sending nnn to the odd part of 3n+13n+13n+1. For every odd mmm with 1<m<3307501 < m < 3307501<m<330750, some iterate of TTT falls strictly below mmm.

This is a descent statement, weaker than convergence: nothing is asserted about where the orbit eventually goes. Its purpose is cycle exclusion, and for that it is exactly the right strength — the minimum of a nontrivial cycle can never descend, so every mmm in this range is disqualified from being a cycle minimum.

Descent is also markedly cheaper to certify than convergence. Below 997819978199781 it is inherited from the existing convergence result, since an orbit reaching 111 from m>1m > 1m>1 has certainly dropped below mmm. Above 997819978199781 it comes from a ladder of independent range lemmas, each of which follows orbits only until their first drop below that range's own lower bound. Half of each range needs no orbit data at all: if m≡1(mod4)m \equiv 1 \pmod 4m≡1(mod4) then 4∣3m+14 \mid 3m+14∣3m+1, so T(m)≤(3m+1)/4<mT(m) \le (3m+1)/4 < mT(m)≤(3m+1)/4<m in a single step.

Preamble
import Mathlib
import Definitions.Def_syracuseStep
Formal statement
theorem syracuse_descends_below_330750 (m : ℕ) (h1 : 1 < m) (hlt : m < 330750) (hodd : Odd m) :
    ∃ t : ℕ, syracuseStep^[t] m < m := by sorry
Source
Collatz mission https://prove2.me/missions/2f34a49f-2016-4de2-9662-fcd1cc96cc67; assembled from syracuse_reaches_one_below_99781 (for m below 99781) and 58 independent descent range lemmas syracuse_descends_range_* covering [99781, 330749].

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