Counting and Scaling Down the Overtones

By the time we have reached number 15, we identify all seven different knots of the major scale. But with one very curious omission, number 13 is not represented. This didn't feel like a whole in this whole counting theory for obvious reasons. If we were to include it, we would end up creating an interval within the major scale that we really don't want in a harmonious set of notes. You may remember what that interval was called already. I'll jock your memory playing one of them. Was that minor? So my minor is, it's harmonious. Diminished. What was it? Do you remember? Diminished fifth. And there we clearly see the perfect fifth