Elsewhere commented. However because of the importance of the only known proofs of optimality of sphere packing in higher dimensions posting here. https://www.quantamagazine.org/sphere-packing-solved-in-higher-dimensions-20160330/ covers the solution to optimality of known sphere packings in dimensions $8$ and $24$ using modular forms and this is one reason why modular forms are interesting as they show up naturally to solve a central problem in an area of mathematics.