Yes 1 exists. It is not a material thing however and instead immaterial. It is an "idea" of sorts, but one that exists nonetheless. Of course it all depends on what we mean by existence of course, but it would be best to apply it in it's broadest sense. In this broad sense clearly, 1 exists. An example of something that doesn't exist or rather and even more strongly, couldn't exist, is 'nothing'. Nothing cannot exist. Nothing, while like 1, being an idea, would still be something, namely an idea. Likewise if 'nothing' did exist somewhere etc. then it would be something and no longer 'nothing'. Some say the set of nothing or the null set would show nothing existing, however that is still a set and not a proper referant of nothing. Remember that nothing has no referant. Simply put you couldn't even think of nothing, you would fail to do so, and further you would fail to be DOING nothing, because you would be engaging in a thought process, namely thinking of nothing. All in all, nothing could not exist, BUT MOST ASSUREDLY NUMBERS EXIST. After all, life and everything for that matter is dictated by physics, and well there's math and numbers involved in that. Similarly math and numbers are real because they are not, as some like to believe, man made or arbitrary. We may NAME them differently or CALL them different names like one and uno or even the symbol 1 and I (roman numeral) however the idea is always the same, the meaning is always the same, 1. So, 2,3,4,5,6,7,8,9, and even 0 exist, and also don't think 0 is nothing, while it is the symbol for the idea of nothing, it itself is a thing and there is no true referant for nothing, because then it would fail to be nothing and be a thing.