To all of you who love math like me, I have this puzzling riddle that I hope you find interesting :
On Christmas Eve just after midnight, Santa was riding his sleigh over the Miracle Sea when suddenly something went wrong and he crashed on a lonely Island.
Although this Island wasn't connected to the outer world, it wasn't completely deserted. It was populated by elves that was both intelligent and rational. But they had one flaw.
Among the elves it was considered a huge shame to have blue eyes. If an elf discovered that she/he had blue eyes, she/he would flee the island in shame the next midnight. You would think that since the elves had lived on the island for generations, there would be no blue eyed elves left, but since there didn't exist any mirrors on the island and the fact that all the elves was so polite, that they would never mention each others eye color, there was actually still some with blue eyes.
Now.. Santa was invited in by the elves and his sleigh was repaired. After three Christmas hours with the elves, which for Santa on Christmas Eve is almost nothing, he was ready to move on. But when he sat up in his sleigh he made the mistake of shouting "Ho! Ho! Ho! It's is so nice to see both blue and brown eyed elves living together. Merry Christmas to all of you!" And then he flew away. The 43'th midnight after Santas visit some of the elves left the island.
How many blue eyed elves was on the island, when Santa crashed?
Merry Christmas to all of you and this exercise is from "Kalkulus" by Tom Lindstrøm, which is a great book :D