<span>The least common multiple is the smallest number that is divisible by each of the numbers being considered. Example: While 15, 30, 45, 60, 75, ... are all commonmultiplies of 3 and 5, 15 is the smallest number divisible by both 3 and 5. It is the leastcommon multiple.</span>
Let <em>f(x)</em> be the sum of the geometric series,

for |<em>x</em>| < 1. Then taking the derivative gives the desired sum,
