The use of "#"

[Tom]

Hi

Could you please tell if if the use of "#" in the sense of "number" i.e, "#4" in a formal style is OK? What about plural--#s 4 and 5? Are the following correct in a formal style? Which one is most natural?

1- Sentence # 6 is incorrect.
2- Sentence no: 6 is incorrect.
3 -Sentences numbers 5 and 6 are incorrect.
4- Sentences #s 5 and 6 are incorrect.

Tom

[Conchita]

I've only seen the sign # for number used by Americans. As to its use in a formal context, let's wait for someone else's opinion.

Personally, and as I've been taught, I try not to use abbreviations in formal writing.

I'd write:

Sentence number/no. 6.
Sentences number/no. 5 and 6 (though the plural 'numbers/nos.' is used too).

[Jamie (K)]