9 27 x 1 81 July 8, 2019 16 32 64 128 9 * 81 x 1 27 x 2 9 27 mũ x 1 81 9 chia 27 mũ x 1 81 9 * 81 x 1 27 x 3 9 2x 1 81 27 x 27 × 9 27 x 9
