Elliptic curve with LMFDB label 256.c2 (Cremona label 256c1)

• Label: 256.c2
• Conductor: $256$
• Discriminant: $-512$
• j-invariant: $1728$
• CM: yes ($D=-4$)
• Rank: $0$
• Torsion structure: $\Z/{2}\Z$

Minimal Weierstrass equation

$y^2=x^3+2x$

(, )

Mordell-Weil group structure

$\Z/{2}\Z$

Mordell-Weil generators

$P$	$\hat{h}(P)$	Order
$(0, 0)$	$0$	$2$

Integral points

$\left(0, 0\right)$

Invariants

Conductor:	$N$	=	$256$	=	$2^{8}$
Discriminant:	$\Delta$	=	$-512$	=	$-1 \cdot 2^{9}$
j-invariant:	$j$	=	$1728$	=	$2^{6} \cdot 3^{3}$
Endomorphism ring:	$\mathrm{End}(E)$	=	$\Z$
Geometric endomorphism ring:	$\mathrm{End}(E_{\overline{\Q}})$	=	$\Z[\sqrt{-1}]$    (potential complex multiplication)
Sato-Tate group:	$\mathrm{ST}(E)$	=	$N(\mathrm{U}(1))$
Faltings height:	$h_{\mathrm{Faltings}}$	≈	$-0.79067254049155053618935099221$
Stable Faltings height:	$h_{\mathrm{stable}}$	≈	$-1.3105329259115095182522750833$
$abc$ quality:	$Q$	≈	$$
Szpiro ratio:	$\sigma_{m}$	≈	$2.4693609377704338$

BSD invariants

Analytic rank:	$r_{\mathrm{an}}$	=	$0$
Mordell-Weil rank:	$r$	=	$0$
Regulator:	$\mathrm{Reg}(E/\Q)$	=	$1$
Real period:	$\Omega$	≈	$3.1181694995108224605795923569$
Tamagawa product:	$\prod_{p}c_p$	=	$2$  = $2$
Torsion order:	$\#E(\Q)_{\mathrm{tor}}$	=	$2$
Special value:	$L(E,1)$	≈	$1.5590847497554112302897961785$
Analytic order of Ш:	Ш${}_{\mathrm{an}}$	=	$1$    (exact)

BSD formula

$\displaystyle 1.559084750 \approx L(E,1) = \frac{\# Ш(E/\Q)\cdot \Omega_E \cdot \mathrm{Reg}(E/\Q) \cdot \prod_p c_p}{\#E(\Q)_{\rm tor}^2} \approx \frac{1 \cdot 3.118169 \cdot 1.000000 \cdot 2}{2^2} \approx 1.559084750$

Modular invariants

Modular form   256.2.a.c

$q + 4 q^{5} - 3 q^{9} + 4 q^{13} - 2 q^{17} + O(q^{20})$

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

Modular degree:	8
$\Gamma_0(N)$-optimal:	yes
Manin constant:	1

Local data at primes of bad reduction

This elliptic curve is not semistable. There is only one prime $p$ of bad reduction:

$p$	Tamagawa number	Kodaira symbol	Reduction type	Root number	$\mathrm{ord}_p(N)$	$\mathrm{ord}_p(\Delta)$	$\mathrm{ord}_p(\mathrm{den}(j))$
$2$	$2$	$III$	additive	-1	8	9	0

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	16.384.9.817

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
$2$	additive	$4$	$1$

Isogenies

This curve has non-trivial cyclic isogenies of degree $d$ for $d=$ 2.
Its isogeny class 256.c consists of 2 curves linked by isogenies of degree 2.

Twists

The minimal quadratic twist of this elliptic curve is 256.b2, its twist by $8$.

The minimal quartic twist of this elliptic curve is 32.a3, its quartic twist by $-8$.

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:

$[K:\Q]$	$K$	$E(K)_{\rm tors}$	Base change curve
$2$	$\Q(\sqrt{-2})$	$\Z/2\Z \oplus \Z/2\Z$	2.0.8.1-1024.1-b2
$4$	4.2.2048.1	$\Z/4\Z$	not in database
$8$	8.0.16777216.2	$\Z/4\Z \oplus \Z/4\Z$	not in database
$8$	8.4.67108864.1	$\Z/8\Z$	not in database
$8$	8.0.67108864.1	$\Z/8\Z$	not in database
$8$	8.2.36691771392.4	$\Z/6\Z$	not in database
$8$	8.0.2097152000.7	$\Z/10\Z$	not in database
$16$	16.0.18014398509481984.1	$\Z/8\Z \oplus \Z/8\Z$	not in database
$16$	16.4.4611686018427387904.2	$\Z/16\Z$	not in database
$16$	16.0.1346286087882789617664.2	$\Z/3\Z \oplus \Z/6\Z$	not in database
$16$	deg 16	$\Z/10\Z$	not in database
$16$	16.0.5385144351531158470656.26	$\Z/2\Z \oplus \Z/6\Z$	not in database
$16$	deg 16	$\Z/2\Z \oplus \Z/10\Z$	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

$p$	2
Reduction type	add
$\lambda$-invariant(s)	-
$\mu$-invariant(s)	-

All Iwasawa $\lambda$ and $\mu$-invariants for primes $p\ge 3$ of good reduction are zero.

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

$p$-adic regulators

All $p$-adic regulators are identically $1$ since the rank is $0$.