Can I say na, nano, nanu as "seven" instead of nana? On my kanji dictionary, below , there are several kunyomi among the common ones ( _nana_ , _nanatsu_ ), they are: _na_ , _nano_ , _nanu_ ; it's written that they are nouns themselves and it's the same for the other numbers (for example, _fuu_ for , _mi_ for , _mu_ for , etc.; they're all nouns). So, when does someone say _na_ , _nano_ , _nanu_ as a noun alone for "seven" instead of _shichi_ / _nana_? Did they do it in the past?

No, I think very few people will understand you if you say or individually to mean "seven". Although they are listed as readings, they only make sense when the are in compounds. If you look up or "seven" (as a word) in a dictionary, the only pronunciations that appear will be and , which is dialectical.

Although they are listed as readings of the kanji, they will only make sense in compounds. is used in , which means the "seventh day of the month. is obscure and also seen in . I have never even heard it pronounced this way. is not even listed in as a pronunciation. I recommend that you remember the pronunciation of words and kanji compounds rather than the pronunciations of a single Kanji.