Minimal Weierstrass equation
magma: E := EllipticCurve("20a4");
sage: E = EllipticCurve("20a4")
gp: E = ellinit("20a4")
\( y^2 = x^{3} + x^{2} - 41 x - 116 \)
Mordell-Weil group structure
Torsion generators
\( \left(-4, 0\right) \)
Integral points
\( \left(-4, 0\right) \)
Invariants
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magma: Conductor(E);
sage: E.conductor().factor()
gp: ellglobalred(E)[1]
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| Conductor: | \( 20 \) | = | \(2^{2} \cdot 5\) | ||
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magma: Discriminant(E);
sage: E.discriminant().factor()
gp: E.disc
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| Discriminant: | \(2000 \) | = | \(2^{4} \cdot 5^{3} \) | ||
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magma: jInvariant(E);
sage: E.j_invariant().factor()
gp: E.j
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| j-invariant: | \( \frac{488095744}{125} \) | = | \(2^{14} \cdot 5^{-3} \cdot 31^{3}\) | ||
| Endomorphism ring: | \(\Z\) | (no Complex Multiplication) | |||
| Sato-Tate Group: | $\mathrm{SU}(2)$ | ||||
BSD invariants
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magma: Rank(E);
sage: E.rank()
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| Rank: | \(0\) | ||
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magma: Regulator(E);
sage: E.regulator()
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| Regulator: | \(1\) | ||
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magma: RealPeriod(E);
sage: E.period_lattice().omega()
gp: E.omega[1]
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| Real period: | \(1.88291676131\) | ||
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magma: TamagawaNumbers(E);
sage: E.tamagawa_numbers()
gp: gr=ellglobalred(E); [[gr[4][i,1],gr[5][i][4]] | i<-[1..#gr[4][,1]]]
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| Tamagawa product: | \( 1 \) = \( 1\cdot1 \) | ||
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magma: Order(TorsionSubgroup(E));
sage: E.torsion_order()
gp: elltors(E)[1]
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| Torsion order: | \(2\) | ||
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magma: MordellWeilShaInformation(E);
sage: E.sha().an_numerical()
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| Analytic order of Ш: | \(1\) (exact) | ||
Modular invariants
Modular form 20.2.a.a
gp: x*deriv(xy[1])/(2*xy[2]+E.a1*xy[1]+E.a3)
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magma: ModularDegree(E);
sage: E.modular_degree()
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| Modular degree: | 6 | ||
| \( \Gamma_0(N) \)-optimal: | no | ||
| Manin constant: | 2 | ||
Special L-value
sage: E.lseries().dokchitser().derivative(1,r)/r.factorial()
gp: ar[2]/factorial(ar[1])
\( L(E,1) \) ≈ \( 0.470729190327 \)
Local data
| prime | Tamagawa number | Kodaira symbol | Reduction type | Root number | ord(\(N\)) | ord(\(\Delta\)) | ord\((j)_{-}\) |
|---|---|---|---|---|---|---|---|
| \(2\) | \(1\) | \( IV \) | Additive | -1 | 2 | 4 | 0 |
| \(5\) | \(1\) | \( I_{3} \) | Non-split multiplicative | 1 | 1 | 3 | 3 |
Galois representations
The image of the 2-adic representation attached to this elliptic curve is the subgroup of $\GL(2,\Z_2)$ with Rouse label X9c.
This subgroup is the pull-back of the subgroup of $\GL(2,\Z_2/2^3\Z_2)$ generated by $\left(\begin{array}{rr} 1 & 1 \\ 0 & 1 \end{array}\right),\left(\begin{array}{rr} 7 & 0 \\ 2 & 1 \end{array}\right),\left(\begin{array}{rr} 1 & 0 \\ 6 & 3 \end{array}\right)$ and has index 12.
sage: [rho.image_type(p) for p in rho.non_surjective()]
The mod \( p \) Galois representation has maximal image \(\GL(2,\F_p)\) for all primes \( p \) except those listed.
| prime | Image of Galois representation |
|---|---|
| \(2\) | B |
| \(3\) | B.1.2 |
$p$-adic data
$p$-adic regulators
All \(p\)-adic regulators are identically \(1\) since the rank is \(0\).
Iwasawa invariants
| $p$ | 2 | 3 | 5 |
|---|---|---|---|
| Reduction type | add | ordinary | nonsplit |
| $\lambda$-invariant(s) | - | 2 | 0 |
| $\mu$-invariant(s) | - | 1 | 0 |
All Iwasawa $\lambda$ and $\mu$-invariants for primes $p\ge 5$ of good reduction are zero.
An entry - indicates that the invariants are not computed because the reduction is additive.
Isogenies
This curve has non-trivial cyclic isogenies of degree \(d\) for \(d=\)
2, 3 and 6.
Its isogeny class 20a
consists of 4 curves linked by isogenies of
degrees dividing 6.
Growth of torsion in number fields
The number fields $K$ of degree up to 7 such that $E(K)_{\rm tors}$ is strictly larger than $E(\Q)_{\rm tors}$ $\cong \Z/{2}\Z$ are as follows:
| $[K:\Q]$ | $K$ | $E(K)_{\rm tors}$ | Base-change curve |
|---|---|---|---|
| 2 | \(\Q(\sqrt{5}) \) | \(\Z/2\Z \times \Z/2\Z\) | 2.2.5.1-80.1-a6 |
| \(\Q(\sqrt{-3}) \) | \(\Z/6\Z\) | 2.0.3.1-400.1-a4 | |
| 3 | 3.1.108.1 | \(\Z/6\Z\) | Not in database |
| 4 | 4.0.320.1 | \(\Z/4\Z\) | Not in database |
| \(\Q(\sqrt{-3}, \sqrt{5})\) | \(\Z/2\Z \times \Z/6\Z\) | Not in database | |
| 6 | 6.0.34992.1 | \(\Z/3\Z \times \Z/6\Z\) | Not in database |
| 6.2.1458000.2 | \(\Z/2\Z \times \Z/6\Z\) | Not in database |
We only show fields where the torsion growth is primitive. For each field $K$ we either show its label, or a defining polynomial when $K$ is not in the database.