Every so often FB asks me to add my mobile number and pre-fills the field with some number I'm not familiar with. Not mine, nor anyone I know. Perhaps I should

Every so often FB asks me to add my mobile number and pre-fills the field with some number I'm not familiar with. Not mine, nor anyone I know. Perhaps I should celebrate. ;) (I haven't paid attention to whether it's the same number every time I've been asked, though; I probably should, and perhaps do a reverse search on it to see if I can find out who it belongs to.)