Harmonic series (mathematics)
The "worm on the rubber band". Suppose that a worm crawls along an infinitely-elastic one-meter rubber band at the same time as the rubber band is uniformly stretched. If the worm travels 1 centimeter per minute and the band stretches 1 meter per minute, will the worm ever reach the end of the rubber band? The answer, counterintuitively, is "yes", for after  minutes, the ratio of the distance travelled by the worm to the total length of the rubber band is