On elliptic curves with an isogeny of degree 7

R. Greenberg, K. Rubin, A. Silverberg +1

We show that if $E$ is an elliptic curve over $\mathbf{Q}$ with a $\mathbf{Q}$-rational isogeny of degree 7, then the image of the 7-adic Galois representation attached to $E$ is a…