
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
The natural number  $a_n$  is obtained by writing together and ordered, in decimal notation , all natural numbers between  $1$  and  $n$ . So we have for example that  $a_1 = 1$ , $a_2 = 12$ ,  $a_3 = 123$ ,  $. . .$  ,  $a_{11} = 1234567891011$ ,   $...$  . Find all values of  $n$  for which  $a_n$  is not divisible by  $3$ .

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