Fourier coefficients of noncongruence cuspforms
Fourier coefficients of noncongruence cuspforms
Given a finite index subgroup of SL2(ℤ) with modular curve defined over ℚ, under the assumption that the space of weight k (⩾2) cuspforms is one-dimensional, we show that a form in this space with Fourier coefficients in ℚ has bounded denominators if and only if it is a congruence …