Ramanujan's class invariants, Kronecker's limit formula, and modular equations
In his notebooks, Ramanujan gave the values of over 100 class invariants which he had calculated. Many had been previously calculated by Heinrich Weber, b'ut approximately half of them had not been heretofore determined. G. N. Watson wrote several papers devoted to the calculation of , class invariants, but his methods were not entirely rigorous. Up until the past few years, eighteen of Ramanujan's class invariants remained to be verified. Five were verified by the authors in a recent paper. For the remaining class invariants, in each case, the associated imaginary quadratic field has class number 8, and moreover there are two classes per genus. The authors devised three methods to calculate these thirteen class invariants. The first depends upon Kronecker's limit formula, the second employs modular equations, and the third uses class field theory to make Watson's "empirical method"rigorous. ©1997 American Mathematical Society.
Berndt, Bruce, Heng Huat Chan, and Liang-Cheng Zhang. "Ramanujan’s class invariants, Kronecker’s limit formula, and modular equations." Transactions of the American Mathematical Society 349, no. 6 (1997): 2125-2173.
Transactions of the American Mathematical Society