Curve name  $X_{21}$  
Index  $8$  
Level  $4$  
Genus  $0$  
Does the subgroup contain $I$?  Yes  
Generating matrices  $ \left[ \begin{matrix} 1 & 1 \\ 3 & 0 \end{matrix}\right], \left[ \begin{matrix} 1 & 2 \\ 2 & 3 \end{matrix}\right]$  
Images in lower levels 


Meaning/Special name  $X_{ns}(4)$  
Chosen covering  $X_{7}$  
Curves that $X_{21}$ minimally covers  $X_{2}$, $X_{7}$  
Curves that minimally cover $X_{21}$  $X_{59}$  
Curves that minimally cover $X_{21}$ and have infinitely many rational points.  
Model  A model was not computed. This curve is a conic with no rational points.  
Info about rational points  
Comments on finding rational points  None  
Elliptic curve whose $2$adic image is the subgroup  None  
Generic density of odd order reductions  N/A 