There are interesting facts about the life cycle of periodical cicadas. Usually, we do not see around a lot of these insects, because most part of their life they spend under the ground and gently suck the plant roots.
However, depending on the type every 7, 11, 13 or 17 years, periodical cicadas simultaneously crawl out together to the light and they turn into the noisy flying creatures, mate and die soon.
Although our strange cicadas cheerfully go into another world, here arises the obvious question: is it just coincidence or the numbers 7, 11, 13 and 17 some special?
It turns out that these numbers have something in common. They are all prime numbers that are divisible only by themselves and by one (it's 1, 2, 3, 5, 7, 11, 13, 17, 19, 23 and so on).