- An arithmetic progression (AP) is a sequence of numbers where the difference between consecutive terms is constant. - The general form of an AP is: a, a + d, a + 2d, a + 3d, ..., a + (n - 1)d - Where a is the first term and d is the common difference, which is the amount each term increases by. - To find the nth term, the formula is: an = a + (n - 1)d - The sum of the first n terms of an AP can be calculated as: Sn = n/2 * (2a + (n - 1)d)