Subgroups of the modular group generated by parabolic elements of constant amplitude
Subgroups of the modular group defined by a single linear congruence
Generalized Jacobsthal sums and sums of squares
Difference sets
On the representation of a number as the sum of any number of squares, and in particular of twenty
Sums of Powers of Cusp Form Coefficients. II.
The zeros of certain Poincaré series
Burnside's uniformization
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