We study the integer sequence Tk = 6·2k + 1 (OEIS A004119) and establish a complete theory of its modular periodicity, introducing the OMARWA period P(m) framework. 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) = ordm'(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.