Similar puzzles have often embarrass surfers. At first glance, they seem very simple, but in reality you have to think a little to unravel them. This puzzle is very similar. It almost immediately begs for the answer.
Most of you will think that it is about number 6, but it is nothing like that. The puzzle is more difficult than you thought. Try to approach it a bit differently.
Change your way of thinking and think about whether in fact it has to be a number? Perhaps it could be a letter or a symbol?
If, despite the efforts, you have failed to come up with an answer, you will find it on the next page.