Abelian variety isogeny class 2.31.a_cb over $\F_{31}$

• Label: 2.31.a_cb
• Base field: $\F_{31}$
• Dimension: $2$
• $p$-rank: $2$
• Ordinary: yes
• Supersingular: no
• Simple: no
• Geometrically simple: no
• Primitive: yes
• Principally polarizable: yes
• Contains a Jacobian: yes

Invariants

Base field:	$\F_{31}$
Dimension:	$2$
L-polynomial:	$( 1 - 3 x + 31 x^{2} )( 1 + 3 x + 31 x^{2} )$
	$1 + 53 x^{2} + 961 x^{4}$
Frobenius angles:	$\pm0.413172001920$, $\pm0.586827998080$
Angle rank:	$1$ (numerical)
Jacobians:	$38$
Cyclic group of points:	yes

This isogeny class is not simple, primitive, ordinary, and not supersingular. It is principally polarizable and contains a Jacobian.

Newton polygon

This isogeny class is ordinary.

$p$-rank:	$2$
Slopes:	$[0, 0, 1, 1]$

Point counts

Point counts of the abelian variety

$r$	$1$	$2$	$3$	$4$	$5$
$A(\F_{q^r})$	$1015$	$1030225$	$887499760$	$851255343225$	$819628234555375$

Point counts of the curve

$r$	$1$	$2$	$3$	$4$	$5$	$6$	$7$	$8$	$9$	$10$
$C(\F_{q^r})$	$32$	$1068$	$29792$	$921748$	$28629152$	$887495838$	$27512614112$	$852893157988$	$26439622160672$	$819628182129948$

Jacobians and polarizations

This isogeny class is principally polarizable and contains the Jacobians of 38 curves (of which all are hyperelliptic):

• $y^2=6 x^6+24 x^5+9 x^4+x^3+7 x+10$
• $y^2=18 x^6+10 x^5+27 x^4+3 x^3+21 x+30$
• $y^2=29 x^6+29 x^5+18 x^4+14 x^3+13 x^2+29 x+2$
• $y^2=4 x^6+15 x^5+30 x^4+14 x^3+6 x^2+6 x+12$
• $y^2=12 x^6+14 x^5+28 x^4+11 x^3+18 x^2+18 x+5$
• $y^2=25 x^6+19 x^5+19 x^4+14 x^3+14 x^2+22$
• $y^2=13 x^6+26 x^5+26 x^4+11 x^3+11 x^2+4$
• $y^2=20 x^6+10 x^5+9 x^4+7 x^2+16 x+18$
• $y^2=29 x^6+30 x^5+27 x^4+21 x^2+17 x+23$
• $y^2=20 x^6+2 x^5+10 x^4+30 x^3+17 x^2+12 x+13$
• $y^2=29 x^6+6 x^5+30 x^4+28 x^3+20 x^2+5 x+8$
• $y^2=20 x^6+19 x^5+10 x^4+11 x^3+30 x^2+16 x+13$
• $y^2=26 x^6+10 x^5+27 x^4+3 x^3+28 x^2+13 x+12$
• $y^2=16 x^6+30 x^5+19 x^4+9 x^3+22 x^2+8 x+5$
• $y^2=13 x^6+23 x^5+3 x^4+4 x^3+13 x+9$
• $y^2=8 x^6+7 x^5+9 x^4+12 x^3+8 x+27$
• $y^2=20 x^6+27 x^5+23 x^4+18 x^3+16 x^2+15 x+29$
• $y^2=29 x^6+19 x^5+7 x^4+23 x^3+17 x^2+14 x+25$
• $y^2=7 x^6+18 x^5+22 x^4+11 x^3+17 x^2+21 x+1$
• $y^2=21 x^6+23 x^5+4 x^4+2 x^3+20 x^2+x+3$
• and

• $y^2=2 x^6+20 x^5+7 x^4+25 x^3+10 x^2+8$
• $y^2=6 x^6+29 x^5+21 x^4+13 x^3+30 x^2+24$
• $y^2=27 x^6+2 x^5+23 x^4+10 x^3+14 x^2+10 x+4$
• $y^2=15 x^6+18 x^5+22 x^4+5 x^3+2 x^2+25 x+8$
• $y^2=7 x^6+4 x^5+20 x^4+18 x^3+30 x^2+17 x+5$
• $y^2=21 x^6+12 x^5+29 x^4+23 x^3+28 x^2+20 x+15$
• $y^2=30 x^6+12 x^5+13 x^4+27 x^3+4 x^2+27 x+20$
• $y^2=28 x^6+5 x^5+8 x^4+19 x^3+12 x^2+19 x+29$
• $y^2=16 x^6+10 x^5+12 x^4+24 x^3+6 x^2+18 x+2$
• $y^2=17 x^6+30 x^5+5 x^4+10 x^3+18 x^2+23 x+6$
• $y^2=2 x^6+14 x^5+5 x^4+13 x^3+25 x^2+9 x+2$
• $y^2=6 x^6+11 x^5+15 x^4+8 x^3+13 x^2+27 x+6$
• $y^2=8 x^6+13 x^5+8 x^4+9 x^3+20 x^2+27 x+1$
• $y^2=24 x^6+8 x^5+24 x^4+27 x^3+29 x^2+19 x+3$
• $y^2=30 x^6+25 x^5+10 x^4+28 x^3+x^2+2 x+1$
• $y^2=28 x^6+13 x^5+30 x^4+22 x^3+3 x^2+6 x+3$
• $y^2=6 x^6+22 x^5+19 x^4+17 x^3+28 x^2+13 x+3$
• $y^2=18 x^6+4 x^5+26 x^4+20 x^3+22 x^2+8 x+9$

Decomposition and endomorphism algebra

All geometric endomorphisms are defined over $\F_{31^{2}}$.

Endomorphism algebra over $\F_{31}$

The isogeny class factors as 1.31.ad $\times$ 1.31.d and its endomorphism algebra is a direct product of the endomorphism algebras for each isotypic factor. The endomorphism algebra for each factor is:

• 1.31.ad : \(\Q(\sqrt{-115}) \).
• 1.31.d : \(\Q(\sqrt{-115}) \).

Endomorphism algebra over $\overline{\F}_{31}$

The base change of $A$ to $\F_{31^{2}}$ is 1.961.cb^2 and its endomorphism algebra is $\mathrm{M}_{2}($\(\Q(\sqrt{-115}) \)$)$

Base change

This is a primitive isogeny class.

Twists

Below are some of the twists of this isogeny class.

Twist	Extension degree	Common base change
2.31.ag_ct	$2$	(not in LMFDB)
2.31.g_ct	$2$	(not in LMFDB)
2.31.a_acb	$4$	(not in LMFDB)