Most epub3 and maths won't work on any eink ereader. You need epub3 compliant apps on iOS and Android. The Kobos do support some epub3, maybe more if it's a kepub file. I don't know if the N647 even does kepub, it's so prehistoric too old for here:
https://pgaskin.net/KoboStuff/kobofirmware.html
Earliest is the Kobo Touch N905 (3 versions).
The Kobo N647 is also called Kobo Wireless, released 15 October 2010. The Kobo Touch (N905) was a year later (2011) and about the oldest Kobo you want to even think about.
https://help.kobo.com/hc/en-us/artic...or-Kobo-tablet
https://en.wikipedia.org/wiki/Kobo_eReader
and
https://wiki.mobileread.com/wiki/Kobo (This site)
Of course nearly anything will work on a suitable Linux, Mac or Windows desktop/laptop viewer.
Did you embed the fonts and select Publisher font on the Kobo? But maybe the Kobo Wireless N647 / N47 doesn't have that.