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Again the problem is: Calculate the value of: $$\left(2^{156221} - 1\right) \bmod 9$$

I have no idea how to find a solution to this and need help urgently!! Thank you in advance.

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    The powers of $2$, modulo $9$, cycle nicely, with period $6$.2012-11-05
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    Why is this urgent?2012-11-05
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    I have an exam shortly on problems similar to this and I have gotten all of the material down except how to do problems like this.2012-11-05

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