Just following the (ambiguous) specification. Are you looking for numbers from (5,11) that are close to 1 or numbers from (1,5) that are close to 11? I didn't find an API spec and found others using pop so I went ahead with the 2-character savings.
Or am I only supposed to return one number if the "two closest" are both on "the same side" of the search-for number? That wasn't clear to me either so I just went with "return the two closest" without trying to assume a bunch of extra subtle meaning to that phrase. No, I'm not going to produce a version that sometimes returns only one number. (:
(but my friends call me "Tye")