Ramanujan's remarkable product of theta-functions
On pages 338 and 339 in his first notebook, Ramanujan records eighteen values for a certain product of theta-functions depending on two integral parameters m and n. When (m, n) = 1, it can be seen that each of these values is a unit. The purpose of this paper is to establish each of these eighteen values and to prove that under certain general conditions this product is indeed a unit. Lastly, we prove that certain quotients of theta-functions are algebraic integers.
Berndt, Bruce C., Heng Huat Chan, and Liang-Cheng Zhang. "Ramanujan's remarkable product of theta-functions." Proceedings of the Edinburgh Mathematical Society 40, no. 3 (1997): 583-612.
Proceedings of the Edinburgh Mathematical Society