Better than the Internet.
Would it be valid to say b2 and #2 instead of b9 and #9? Seeing the nines makes me think I should skip up an octave for those two notes.
I still can't figure that out. The 9/11/13 's are supposed to refer to the notes an octave above the 2/4/6 's but in practice the two sets are used synonymously, at least when used to specify the tones included within a scale. The distinction only seems to make sense in the context of chord symbols, where Cmaj6 refers to a chord which contains the 1,3,5 and 6, while Cmaj13 contains 1,3,5,7,9,11,13, or at least most of those. In that case the higher numbers indicate a higher ceiling for inclusion of the extension tones.