
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
For all positive integers \( n \) less than or equal to \( 3000 \), define
\[
a_n = \left\{ 
\begin{array}{ll}
15, & \text{if } n \text{ is divisible by } 15 \text{ and } 21;\\
18, & \text{if } n \text{ is divisible by } 21 \text{ and } 14;\\
21, & \text{if } n \text{ is divisible by } 14 \text{ and } 15;\\
0, & \text{otherwise}.
\end{array} \right.
\]
Calculate \( \sum_{n=1}^{3000} a_n \).
A) 1992
B) 2124
C) 2450
D) 3060

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