Miyata is bad at math but he's right this type of factorizations are quite useless, at this level at least.
Maybe they'll tackle integer factorization in a later chapter and ultimately public-key cryptography and it will change from a boxing manga to an IT manga.
Or maybe Mashiba will find a...
I love this manga but this scene is quite bad, it brings very little to the story and Irako having completely recovered and beating both Fujiki and Ushimata is unrealistic even for this manga standards. Also one of the reason I prefer the anime.