e.g. 42
Spell them out like "forty-two".
[the number 42] also works.
Syntax like [42] is the old way to link to a remote Wiki, before
the style [URL] was supported, according to TextFormattingRules.
Writing this page as [Why Does Not Wiki Do Numbers] would have been prefered to the !BumpyCase method, and it could then become [Why Doesn't Wiki Do Numbers], which sounds less silly. On the editing page, btw, there is a little note that tells us: "!BiCapitalization looks silly, use brackets for links." See Guidelines for Links.