
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
A natural number that can be expressed as the difference of the squares of two natural numbers is called a "clever number." For example, $16 = 5^{2} - 3^{2}$, so 16 is a "clever number." What is the 1990th "clever number" in the sequence of natural numbers starting from 1? Please provide an explanation.
(Beijing High School Mathematics Competition, 1990)

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