Frobenius isogeny of an elliptic curve
= Frobenius isogeny of an elliptic curve
{c}
{title2=$\pi$}
= Frobenius isogeny
{c}
{synonym}
For an elliptic curve over $\mathbb F_q$, the Frobenius isogeny sends $(x,y)$ to $(x^q,y^q)$. If $a=q+1-\#E(\mathbb F_q)$, then
$$
\pi^2-[a]\pi+[q]=0.
$$