Charlotte Jackson uses this classic clever technique to pseudo randomize border-radius, making irregular circles for a photo grid.
A cicada is a rather grim looking little bug. You may have heard of them. There is a kind called the Periodical Cicada, which simultaneously emerge in masses every 7, 11, 13 or 17 years; they find a mate and then they die. It's not much of a life.
However, the interesting thing is that these numbers are all prime numbers.