I am reading the article "Mathematicians Chase Moonshine’s Shadow" , and want to follow up on one of its sources "On the Numbers of Representations of a Number as a Sum of $2r$ Squares, Where $2r$ Does not Exceed Eighteen" by J. W. L. Glaisher . Since I can't get my hand on the original, what would be the best book that summarizes the results of ?
After digging through many books, the best I found on the subject are:
- Grosswald, E. (1985). Representations of integers as sums of squares. New York: Springer.
- Moreno, C. J., & Wagstaff, S. S. (2006). Sums of squares of integers. Boca Raton: Chapman & Hall/CRC.
Both books have references to Glaisher and his work. Both books expand on the subject in detail, using results in the field by other mathematicians (besides Glaisher).