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Every odd number above one and below 1883432 has a strictly smaller Syracuse iterate

Proved
syracuse_descends_below_1883432

by Zexuan Liu · Sep 10, 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<18834321 < m < 18834321<m<1883432, some iterate of TTT falls strictly below mmm.

This is a descent statement, deliberately weaker than convergence, and exactly the strength cycle exclusion requires: the minimum of a nontrivial cycle can never descend.

Below 150544915054491505449 the result is inherited from the previous descent bound. Above it, the statement comes from a ladder of 195195195 mutually independent range lemmas, each following orbits only until their first drop below that range's own lower bound. Half of every 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_1883432 (m : ℕ) (h1 : 1 < m) (hlt : m < 1883432) (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_descends_below_1505449 and 195 independent descent range lemmas covering [1505449, 1883431].

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