sage:from sage.modular.dirichlet import DirichletCharacter
H = DirichletGroup(840, base_ring=CyclotomicField(12))
chi = DirichletCharacter(H, H._module([0, 0, 0, 9, 2]))
N = Newforms(chi, 2, names="a")
magma://Please install CHIMP (https://github.com/edgarcosta/CHIMP) if you want to run this code
chi := DirichletCharacter("840.73");
S:= CuspForms(chi, 2);
N := Newforms(S);
This newform subspace can be constructed as the kernel of the linear operator
\( T_{13}^{48} + 16 T_{13}^{47} + 128 T_{13}^{46} + 456 T_{13}^{45} + 3786 T_{13}^{44} + \cdots + 1186042971136 \)
acting on \(S_{2}^{\mathrm{new}}(840, [\chi])\).