Canad. Math. Bull. 52(2009), 53-62
Printed: Mar 2009
Let $f$ be a square-free integer and denote by $\Gamma_0(f)^+$ the
normalizer of $\Gamma_0(f)$ in $\SL(2,\R)$. We find the analogues of
the cusp form $\Delta$ for the groups $\Gamma_0(f)^+$.
11F03 - Modular and automorphic functions
11F22 - Relationship to Lie algebras and finite simple groups
30F35 - Fuchsian groups and automorphic functions [See also 11Fxx, 20H10, 22E40, 32Gxx, 32Nxx]