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Every odd number below 6725 reaches one under the Syracuse map

Proved
syracuse_reaches_one_below_6725

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≤67241 \le m \le 67241≤m≤6724 there is a k≥0k \ge 0k≥0 with Tk(m)=1T^k(m) = 1Tk(m)=1.

This is a finite verification. The 336233623362 odd starting values below 672567256725 have orbits meeting 525852585258 distinct odd numbers in total, the largest being 271787327178732717873, and every one of those orbits terminates at 111.

Its role is to supply the small-value input to the margin criterion for excluding Syracuse cycles: combined with the fact that a periodic point whose orbit reaches 111 must equal 111, it shows no nontrivial Syracuse cycle contains a value below 672567256725, which in turn excludes every cycle of period at most 199199199.

Preamble
import Mathlib
import Definitions.Def_syracuseStep
Formal statement
theorem syracuse_reaches_one_below_6725 (m : ℕ) (hm : 0 < m) (hodd : Odd m) (hle : m ≤ 6724) :
    ∃ k : ℕ, syracuseStep^[k] m = 1 := by sorry
Source
Collatz mission https://prove2.me/missions/2f34a49f-2016-4de2-9662-fcd1cc96cc67; extension of syracuse_reaches_one_below_1193 (8771b7ae-8b1e-4838-bc0e-3a832f941d33) from bound 1192 to bound 6724. Orbit data agrees with the standard 3x+1 tables, cf. J. C. Lagarias, The 3x+1 Problem and Its Generalizations, Amer. Math. Monthly 92 (1985), Section 2.

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