Arithmetic progression is one of the simpler types of series in mathematics. It is usually in the form of a, a + d, a + 2d, a + 3d, and so on, in which a is the first term and d is the constant difference between the two successive terms. A progression is also seen as these numbers are added, as in a + (a + d) + (a + 2d) + (a + 3d) +,…, (a + [n + 1]d). An example of an arithmetic progression would be 2 + 6 + 10 + 14 + …, in which d is equal to 4.