
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
Construct a sequence of numbers where the first number is $1$, and for all $n \geq 2$, the sum of the first $n$ numbers in the sequence equals $n^2 + 2n$. The task is to find the sum of the third and the seventh numbers in the sequence.
A) 21
B) 20
C) 22
D) 23
E) 24

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