2, 6, 12, 20, 30, 42, 56, ? What is the missing number?

Each term is n(n+1): 1x2, 2x3, 3x4, ..., 7x8 = 56, so the next term is 8x9 = 72. The differences 4, 6, 8, 10, 12, 14 confirm that the next difference is 16.