
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 a number composed of the digits $1, 2, 3, 4, 5$ with at least 3 digits, how many such $n$-digit numbers have the property that the digits 1 and 2 are not adjacent? Let this number be denoted as $a_n$. Find $a_n$ as well as $a_5$.

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