[endofanera7]

Originally Posted by radix

This is so easy to figure out, but kind of hard to explain. The best way to explain it is that if you follow the rules, they all point to the same symbol. E.g:

11 - ( 1 + 1 ) = 9 = 9 * 1
23 - ( 2 + 3 ) = 18 = 9 * 2
36 - ( 3 + 6 ) = 27 = 9 * 3

[...]

65 - ( 6 + 5 ) = 54 = 9 * 6
76 - ( 7 + 6 ) = 63
77 - ( 7 + 7 ) = 63

86 - ( 8 + 6 ) = 72
87 - ( 8 + 7 ) = 72
88 - ( 8 + 8 ) = 72

Notice that the results of following the rules always results in a multiple of 9? Now all you have to do is make the symbols for the series 9,18,27,36,45,54 identical and I've "guessed" your number.

http://artlung.com/words/flash-psychic-proof/