
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
Group the set of positive odd numbers $\{1,3,5, \cdots\}$ from smallest to largest, with the $n$-th group containing $(2n-1)$ odd numbers. For example, the first group is $\{1\}$, the second group is $\{3,5,7\}$, the third group is $\{9,11,13,15,17\}$, etc. Determine which group contains the number 1991.

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