
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
Let the sequence $\{a_n\}$ satisfy $a_1 + 2a_2 = 3$, and for any $n \in \mathbb{N}^*$, the points $\{P_n(n, a_n)\}$ always satisfy $PP_{n+1} = (1, 2)$. Then, the sum of the first $n$ terms of the sequence $\{a_n\}$, $S_n$, is \_\_\_\_\_\_.

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