We study the integer sequence Tₖ = 6·2ᵏ + 1 (OEIS A004119) and establish a complete theory of its modular periodicity. For each positive integer m, we define the OMARWA period P (m) as the minimal period of the sequence Tₖ mod m, and prove the Core Reduction Theorem: P (m) = ord₌' (2) where m' = m/gcd (m, 6). We derive fractal period laws, a super-period L = 30 via three independent paths, and observe coincidences with exceptional Lie-theoretic Coxeter numbers. All principal theorems are formally verified in Lean 4 with Mathlib (654 declarations, zero sorry axioms, 25 modules). Software DOI: 10. 5281/zenodo. 19024222.
Ömer Çetintaş (Sat,) studied this question.