3 n 2 18 July 8, 2019 16 32 64 128 N 3 2n 2 9n 18 0 180 n 3 )/ 2 3n 3 18n 2 15n 3 3n 2 )= 5n 18 3n 3 4n 2 18n 24 2 3 n 6 )=- 18 N 3 2n 2 9n 18