2 a b 4 c 9 July 8, 2019 16 32 64 128 A 2 b 9 c 7 d 4 Cho a 2 3 b 9 4 c 5 m A 3 2 b 4 2 c 9 2 0 Cho a 2 3 b 9 4 c 5 y