The fundamental = 1st harmonic is not an overtone!
Fundamental frequency = 1st harmonic.
2nd harmonic = 1st overtone.
3rd harmonic = 2nd overtone.
4th harmonic = 3rd overtone.
5th harmonic = 4th overtone.
6th harmonic = 5th overtone.
Look at the link: "Calculations of Harmonics from Fundamental Frequency"
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