3 5 9 x 18 July 8, 2019 16 32 64 128 X 9 1 3 5 18 6 (- 9 ) x 5 18 (- 3 3 5 x 20 18 chia 2 9 1 15 3 5 x 90 3 x 3 = 9 3 5×18