I'm with Gerard, I've been a math geek most of my life... so thank you for bringing this up!!!
I see tons of numerical relationships when I'm
trying to read music... lol
But aside from "
how many quarter notes + how many 16th notes"... kinda thing, I found something much more basic, but still very mathmatical, that really made a huge difference how I play.
I really like what you said:
"And some say that seeing a nice symmetrical and beautiful mathematical expression gives the same kind of experience as hearing a beautiful symphony. I can feel like that myself. Mathematical beauty and musical beauty have many similarities." When I started playing, really playing, and still had the $$$...

I bought up almost all the "Idiot's Guides" pertaining to music I could find: Theory, Composition, Soloing and Improv... etc, etc
I have all of them except one...I saw the Idiot's Guide to Music History" last time I was at the music store and I must have it someday...hehehe
Anyway, when I was reading on how a song is actually structured into beats, measures and lines, it all started to click into place. And the weird thing is I don't think I would have been able to do this back in High School... my real bad geek days.
Until this point when I played something, although I tried to make it sound good, it was still just a sort of rambling series of notes... there was no structure to it, no pattern. Just pretty flute notes.
But like I said, when I sat and thought about it... and I'm talking days of just letting it roll around in my head... it all began to really make sense. And when I was playing, almost without trying I found when I played there was a form to it now.. I was almost instinctivly counding off notes in my head, paying attention to how many measures I had played and knowing now when to repeat the beginning line...
It made a huge difference to how I approach playing something. Almost overnight suff I was making up had form and symetry and sounded amazing compaired to before. Now granted I still have a ton to learn, but talk about a defining monent... this was it!
This was when I began to wonder if I could actually get good at playing these wonderful things.