Form n-400 or n-600?

[Aristea Beltrame]

Hello everyone. I would like to explain to you an unusual case of mine.

I was born abroad in July 1997. In January 2015, my stepmother, who is an American citizen since 2005, has applied for my permanent resident (when I was 17 years old) and my father was not a U.S. citizen yet. My father becomes a U.S. citizen 30 days before I turn 18 years old, and my green card was approved in October 2015. If I want to apply for U.S. citizenship should I file Form N-400 or Form N-600 and why?

I would appreciate some help to understand carefully this problem!
Thank you so much!
Best,
A.

[Donald_Trump]

Aristea Beltrame If you have a greencard, then you need to apply N400.

[newacct]

Aristea Beltrame If you have a greencard, then you need to apply N400.

This is not true. A permanent resident under 18 living in the US in the custody of a US citizen parent automatically becomes a US citizen, in which case they would not (and cannot) file N-400 since they are already a US citizen.

The piece of information missing from the OP's description is whether they became a permanent resident (i.e. got their green card) before or after they turned 18.