If each term of a geometric progression \(a_{1},a_{2},a_{3}\),\\ \(\ \) with \(a_{1} = \frac{1}{8}\) and \(a_{2} \neq a_{1}\), is the arithmetic mean of the next two terms and \(S_{n} = a_{1} + a_{2} + \ldots\ldots + a_{n}\), then \(S_{20} - S_{18}\) is equal to\