17/1, the 17th harmonic, is the harmonic past 16/1 and before 18/1. It is about four octaves and a semitone in size. Used in harmony, it sounds particularly wide: if the lower note is C2, the higher note will be about C#6 or Db6. Think of a soprano and a bass at their extremes. It is however, the basis of 17-limit harmony, as many 17-limit intervals are the difference between this and another harmonic.