I'm not, or I am not. Please also see ell.se. In English, amn't is only used in some Scottish dialects, I believe; see here
– jimsugMay 11 '14 at 13:23
I'm not. Inverted aren't I is standard, but **I aren't* is not. I ain't is nonstandard but generally recognized. In some dialects I amn't is possible, but not generally.
– May 11 '14 at 14:29