
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given an arithmetic sequence ${a_n}$ with a non-zero common difference, its first term $a_1$ is 1, and $a_1$, $a_2$, $a_6$ form a geometric sequence.
(I) Find the general term formula of the sequence ${a_n}$;
(II) Denote $b_n$ as $\frac{1}{a_n a_{n+1}}$, find the sum of the first $n$ terms, $S_n$, of the sequence ${b_n}$.

Present the answer in LaTex format: \boxed{Your answer}
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