
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
Professor M. A. Luco wrote on the board the expression:

$$
\frac{n^{2}-5 n+4}{n-4}
$$

Then, he tells the students that $n$ can be any natural number, except for 4.

a) What is the value of the expression for $n=1$?

b) Marcos substituted $n$ with a natural number and found that the value of the expression is 5. What number did Marcos use for $n$?

c) Which natural numbers cannot be the numerical value of the expression?

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