Here are what I remember:
It is either a post on a rather famous blog or maybe an arxiv paper. Pretty sure it was a post.
Regarding the contents (I don't quite remember that well so there might be inconsistencies), it had a fictional story about two students who for a project invented a new form of cryptology. The two students will each write down a positive integer on a piece of paper, and not tell each other, and the students were supposed to figure out what each others' number was.
One student then repeatedly asks the other "do you know my number?", to which the other student initially repeatedly replies "no". No other words than those two sentences are ever exchanged. At one point, one of the two students will then exclaim that they know the two numbers, and proceed to correctly identify their partner's number.
Thanks in advance!
Are you aware of the function of the symbol "." on Google search?
What it does is it searches for whatever is inbetween " " EXACTLY has you write it.
For instance if you type: "the hungry rabbit jumps" all the results will contain that finite sequence of words in that exact order.
Doing that to: "write down a positive integer on a piece of paper" I was able to find this: http://www.theforumsite.com/forum/topic//44324/0/newest
Hope it is what you were looking for or at least close enough.
If it isn't, just try to remember an exact sequence of words and search for it between " ".