# Properties

 Label 855.b2 Conductor $855$ Discriminant $-98688375$ j-invariant $$\frac{357911}{135375}$$ CM no Rank $1$ Torsion structure $$\Z/{2}\Z$$

# Related objects

Show commands: Magma / Oscar / PariGP / SageMath

## Simplified equation

 $$y^2+xy+y=x^3-x^2+13x+474$$ y^2+xy+y=x^3-x^2+13x+474 (homogenize, simplify) $$y^2z+xyz+yz^2=x^3-x^2z+13xz^2+474z^3$$ y^2z+xyz+yz^2=x^3-x^2z+13xz^2+474z^3 (dehomogenize, simplify) $$y^2=x^3+213x+30566$$ y^2=x^3+213x+30566 (homogenize, minimize)

comment: Define the curve

sage: E = EllipticCurve([1, -1, 1, 13, 474])

gp: E = ellinit([1, -1, 1, 13, 474])

magma: E := EllipticCurve([1, -1, 1, 13, 474]);

oscar: E = elliptic_curve([1, -1, 1, 13, 474])

sage: E.short_weierstrass_model()

magma: WeierstrassModel(E);

oscar: short_weierstrass_model(E)

## Mordell-Weil group structure

$$\Z \oplus \Z/{2}\Z$$

magma: MordellWeilGroup(E);

### Infinite order Mordell-Weil generator and height

 $P$ = $$\left(2, 21\right)$$ (2, 21) $\hat{h}(P)$ ≈ $0.36323771516950845224671678716$

sage: E.gens()

magma: Generators(E);

gp: E.gen

## Torsion generators

$$\left(-7, 3\right)$$

comment: Torsion subgroup

sage: E.torsion_subgroup().gens()

gp: elltors(E)

magma: TorsionSubgroup(E);

oscar: torsion_structure(E)

## Integral points

$$\left(-7, 3\right)$$, $$\left(-3, 21\right)$$, $$\left(-3, -19\right)$$, $$\left(2, 21\right)$$, $$\left(2, -24\right)$$, $$\left(12, 41\right)$$, $$\left(12, -54\right)$$, $$\left(74, 597\right)$$, $$\left(74, -672\right)$$

comment: Integral points

sage: E.integral_points()

magma: IntegralPoints(E);

## Invariants

 Conductor: $$855$$ = $3^{2} \cdot 5 \cdot 19$ comment: Conductor  sage: E.conductor().factor()  gp: ellglobalred(E)[1]  magma: Conductor(E);  oscar: conductor(E) Discriminant: $-98688375$ = $-1 \cdot 3^{7} \cdot 5^{3} \cdot 19^{2}$ comment: Discriminant  sage: E.discriminant().factor()  gp: E.disc  magma: Discriminant(E);  oscar: discriminant(E) j-invariant: $$\frac{357911}{135375}$$ = $3^{-1} \cdot 5^{-3} \cdot 19^{-2} \cdot 71^{3}$ comment: j-invariant  sage: E.j_invariant().factor()  gp: E.j  magma: jInvariant(E);  oscar: j_invariant(E) Endomorphism ring: $\Z$ Geometric endomorphism ring: $$\Z$$ (no potential complex multiplication) sage: E.has_cm()  magma: HasComplexMultiplication(E); Sato-Tate group: $\mathrm{SU}(2)$ Faltings height: $0.21307239548821988223980462814\dots$ gp: ellheight(E)  magma: FaltingsHeight(E);  oscar: faltings_height(E) Stable Faltings height: $-0.33623374884583496345781799032\dots$ magma: StableFaltingsHeight(E);  oscar: stable_faltings_height(E) $abc$ quality: $0.9519686961908224\dots$ Szpiro ratio: $3.8305847731743783\dots$

## BSD invariants

 Analytic rank: $1$ sage: E.analytic_rank()  gp: ellanalyticrank(E)  magma: AnalyticRank(E); Regulator: $0.36323771516950845224671678716\dots$ comment: Regulator  sage: E.regulator()  G = E.gen \\ if available matdet(ellheightmatrix(E,G))  magma: Regulator(E); Real period: $1.4708261858568346289796842454\dots$ comment: Real Period  sage: E.period_lattice().omega()  gp: if(E.disc>0,2,1)*E.omega[1]  magma: (Discriminant(E) gt 0 select 2 else 1) * RealPeriod(E); Tamagawa product: $12$  = $2\cdot3\cdot2$ comment: Tamagawa numbers  sage: E.tamagawa_numbers()  gp: gr=ellglobalred(E); [[gr[4][i,1],gr[5][i][4]] | i<-[1..#gr[4][,1]]]  magma: TamagawaNumbers(E);  oscar: tamagawa_numbers(E) Torsion order: $2$ comment: Torsion order  sage: E.torsion_order()  gp: elltors(E)[1]  magma: Order(TorsionSubgroup(E));  oscar: prod(torsion_structure(E)[1]) Analytic order of Ш: $1$ ( rounded) comment: Order of Sha  sage: E.sha().an_numerical()  magma: MordellWeilShaInformation(E); Special value: $L'(E,1)$ ≈ $1.6027786294863581941559613880$ comment: Special L-value  r = E.rank(); E.lseries().dokchitser().derivative(1,r)/r.factorial()  gp: [r,L1r] = ellanalyticrank(E); L1r/r!  magma: Lr1 where r,Lr1 := AnalyticRank(E: Precision:=12);

## BSD formula

$\displaystyle 1.602778629 \approx L'(E,1) = \frac{\# Ш(E/\Q)\cdot \Omega_E \cdot \mathrm{Reg}(E/\Q) \cdot \prod_p c_p}{\#E(\Q)_{\rm tor}^2} \approx \frac{1 \cdot 1.470826 \cdot 0.363238 \cdot 12}{2^2} \approx 1.602778629$

# self-contained SageMath code snippet for the BSD formula (checks rank, computes analytic sha)

E = EllipticCurve(%s); r = E.rank(); ar = E.analytic_rank(); assert r == ar;

Lr1 = E.lseries().dokchitser().derivative(1,r)/r.factorial(); sha = E.sha().an_numerical();

omega = E.period_lattice().omega(); reg = E.regulator(); tam = E.tamagawa_product(); tor = E.torsion_order();

assert r == ar; print("analytic sha: " + str(RR(Lr1) * tor^2 / (omega * reg * tam)))

/* self-contained Magma code snippet for the BSD formula (checks rank, computes analyiic sha) */

E := EllipticCurve(%s); r := Rank(E); ar,Lr1 := AnalyticRank(E: Precision := 12); assert r eq ar;

sha := MordellWeilShaInformation(E); omega := RealPeriod(E) * (Discriminant(E) gt 0 select 2 else 1);

reg := Regulator(E); tam := &*TamagawaNumbers(E); tor := #TorsionSubgroup(E);

assert r eq ar; print "analytic sha:", Lr1 * tor^2 / (omega * reg * tam);

## Modular invariants

$$q - q^{2} - q^{4} + q^{5} - 2 q^{7} + 3 q^{8} - q^{10} + 2 q^{11} - 4 q^{13} + 2 q^{14} - q^{16} - 2 q^{17} - q^{19} + O(q^{20})$$

comment: q-expansion of modular form

sage: E.q_eigenform(20)

\\ actual modular form, use for small N

[mf,F] = mffromell(E)

Ser(mfcoefs(mf,20),q)

\\ or just the series

Ser(ellan(E,20),q)*q

magma: ModularForm(E);

For more coefficients, see the Downloads section to the right.

Modular degree: 192
comment: Modular degree

sage: E.modular_degree()

gp: ellmoddegree(E)

magma: ModularDegree(E);

$\Gamma_0(N)$-optimal: yes
Manin constant: 1
comment: Manin constant

magma: ManinConstant(E);

## Local data

This elliptic curve is not semistable. There are 3 primes $p$ of bad reduction:

$p$ Tamagawa number Kodaira symbol Reduction type Root number $v_p(N)$ $v_p(\Delta)$ $v_p(\mathrm{den}(j))$
$3$ $2$ $I_{1}^{*}$ additive -1 2 7 1
$5$ $3$ $I_{3}$ split multiplicative -1 1 3 3
$19$ $2$ $I_{2}$ nonsplit multiplicative 1 1 2 2

comment: Local data

sage: E.local_data()

gp: ellglobalred(E)[5]

magma: [LocalInformation(E,p) : p in BadPrimes(E)];

oscar: [(p,tamagawa_number(E,p), kodaira_symbol(E,p), reduction_type(E,p)) for p in bad_primes(E)]

## Galois representations

The $\ell$-adic Galois representation has maximal image for all primes $\ell$ except those listed in the table below.

prime $\ell$ mod-$\ell$ image $\ell$-adic image
$2$ 2B 2.3.0.1

comment: mod p Galois image

sage: rho = E.galois_representation(); [rho.image_type(p) for p in rho.non_surjective()]

magma: [GaloisRepresentation(E,p): p in PrimesUpTo(20)];

gens = [[781, 4, 422, 9], [1, 2, 2, 5], [1, 4, 0, 1], [289, 856, 284, 855], [1137, 4, 1136, 5], [1, 0, 4, 1], [382, 1, 379, 0], [3, 4, 8, 11], [914, 1, 683, 0]]

GL(2,Integers(1140)).subgroup(gens)

Gens := [[781, 4, 422, 9], [1, 2, 2, 5], [1, 4, 0, 1], [289, 856, 284, 855], [1137, 4, 1136, 5], [1, 0, 4, 1], [382, 1, 379, 0], [3, 4, 8, 11], [914, 1, 683, 0]];

sub<GL(2,Integers(1140))|Gens>;

The image $H:=\rho_E(\Gal(\overline{\Q}/\Q))$ of the adelic Galois representation has level $$1140 = 2^{2} \cdot 3 \cdot 5 \cdot 19$$, index $12$, genus $0$, and generators

$\left(\begin{array}{rr} 781 & 4 \\ 422 & 9 \end{array}\right),\left(\begin{array}{rr} 1 & 2 \\ 2 & 5 \end{array}\right),\left(\begin{array}{rr} 1 & 4 \\ 0 & 1 \end{array}\right),\left(\begin{array}{rr} 289 & 856 \\ 284 & 855 \end{array}\right),\left(\begin{array}{rr} 1137 & 4 \\ 1136 & 5 \end{array}\right),\left(\begin{array}{rr} 1 & 0 \\ 4 & 1 \end{array}\right),\left(\begin{array}{rr} 382 & 1 \\ 379 & 0 \end{array}\right),\left(\begin{array}{rr} 3 & 4 \\ 8 & 11 \end{array}\right),\left(\begin{array}{rr} 914 & 1 \\ 683 & 0 \end{array}\right)$.

Input positive integer $m$ to see the generators of the reduction of $H$ to $\mathrm{GL}_2(\Z/m\Z)$:

The torsion field $K:=\Q(E[1140])$ is a degree-$22693478400$ Galois extension of $\Q$ with $\Gal(K/\Q)$ isomorphic to the projection of $H$ to $\GL_2(\Z/1140\Z)$.

The table below list all primes $\ell$ for which the Serre invariants associated to the mod-$\ell$ Galois representation are exceptional.

$\ell$ Reduction type Serre weight Serre conductor
$2$ good $2$ $$45 = 3^{2} \cdot 5$$
$3$ additive $8$ $$19$$
$5$ split multiplicative $6$ $$171 = 3^{2} \cdot 19$$
$19$ nonsplit multiplicative $20$ $$45 = 3^{2} \cdot 5$$

## Isogenies

gp: ellisomat(E)

This curve has non-trivial cyclic isogenies of degree $d$ for $d=$ 2.
Its isogeny class 855.b consists of 2 curves linked by isogenies of degree 2.

## Twists

The minimal quadratic twist of this elliptic curve is 285.b2, its twist by $-3$.

## Growth of torsion in number fields

The number fields $K$ of degree less than 24 such that $E(K)_{\rm tors}$ is strictly larger than $E(\Q)_{\rm tors}$ $\cong \Z/{2}\Z$ are as follows:

 $[K:\Q]$ $E(K)_{\rm tors}$ Base change curve $K$ $2$ $$\Q(\sqrt{-15})$$ $$\Z/2\Z \oplus \Z/2\Z$$ not in database $4$ 4.2.86640.2 $$\Z/4\Z$$ not in database $8$ 8.0.1688960160000.18 $$\Z/2\Z \oplus \Z/4\Z$$ not in database $8$ 8.0.65792250000.7 $$\Z/2\Z \oplus \Z/4\Z$$ not in database $8$ 8.2.23085974187.4 $$\Z/6\Z$$ not in database $16$ deg 16 $$\Z/8\Z$$ not in database $16$ deg 16 $$\Z/2\Z \oplus \Z/6\Z$$ not in database

We only show fields where the torsion growth is primitive. For fields not in the database, click on the degree shown to reveal the defining polynomial.

## Iwasawa invariants

 $p$ Reduction type $\lambda$-invariant(s) $\mu$-invariant(s) 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 ord add split ord ord ord ord nonsplit ord ord ss ss ss ord ord 2 - 2 1 1 1 1 1 1 1 1,1 1,1 1,1 1 1 0 - 0 0 0 0 0 0 0 0 0,0 0,0 0,0 0 0

An entry - indicates that the invariants are not computed because the reduction is additive.

## $p$-adic regulators

Note: $p$-adic regulator data only exists for primes $p\ge 5$ of good ordinary reduction.