# Finding patterns

1. Feb 20, 2009

### daniel_i_l

Suppose I have a random binary number of length n>3 and another binary number of length 3 which we will call the "pattern". What are the chances that the pattern will appear in the number such that the spacing between the digits in the pattern are equal? For example, if the pattern is 101 then it appears in 11001 (starting with the first digit and spacing of 1) but not in 111110000.
My first thought was to calculate the chance of finding the pattern starting with a certain digit together with a certain spacing and using that, calculate the probability of finding the pattern in one of the many configurations (configuration = starting point together with spacing). The problem is that some configurations are mutually exclusive - finding one lowers the chances of finding the other one while some are the opposite. How can I take these considerations into account?
Thanks.

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