If you take a number, and count the letters used to spell that number, you’ll get another one. Repeating this process will take you, in english, to 4, but if you write the numbers in spanish, there are two options, described in the picture.
Pick a number between 1 and 99, write it as a word, then count the letters to get a new number. Write the new number as a word, and count its letters- repeat. This curiosity was tweeted by @IanMathmogician, and if you try it you’ll find you get stuck at the number 4- the only number equal to its letter-count. This image shows the network of what your possible routes to 4 could be. It shows you’ll always get there after 5 steps. [code] [French version] [full size image]