Frobenius isogeny of an elliptic curve (source code)

= Frobenius isogeny of an elliptic curve
{c}
{title2=$\pi$}
{wiki=Frobenius_endomorphism#As_an_arithmetic_Frobenius}

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
$$
\pi^2-[a]\pi+[q]=0.
$$