2 3 n 4 12 July 8, 2019 16 32 64 128 1 2 3 4 n =- 1 12 1 2 3 4 n 120 2 3 4 n 8 1 4n 12 simplified Proof 1 2 3 4 n =- 1 12 2 3 4 n 8 1 4 n 12 1 2 3 4 5 n 1275 2 3 n 1 2 + 3 4 2 3+4