Solve congruence equation (13*2)(15*2)(17*2)....(27*2)(29*2) == a (modulo 8); least positive residue

Pi Product notation compact way of representing this modular arithmetic or congruence equation modulo 8. @misterwootube presented a lucid and instructional lesson October 22 2015 detailing the advantage of said notation. Helpful Lemma is any odd number squared is congruent to 1 mod 8