Newform orbit 256.2.a.a

$q$-expansion

$q - 2q^{3} + q^{9} - 6q^{11} - 6q^{17} - 2q^{19} + O(q^{25})$

Coefficient field

The coefficients $a_n$ generate $\mathbb{Q}$. The eigenvalue of $T = T_{3} + 3T_{5}$ is a root of

$x + 2$

Complex multiplication by $\mathbb{Q}(\sqrt{-8})$: $a_p = 0$ for every conjugate at the 6 primes $p \le 31$ inert in it (exactly, from $\operatorname{tr} a_{p^2} = -\dim \cdot p^{k-1}$), and $\operatorname{tr} a_p = 0$ at all 86 inert primes $p < 1000$. This is evidence from the stored coefficients, not a proof.

Atkin–Lehner signs

For $p \parallel N$ every form in the orbit has $a_p = -p^{k/2-1} w_p$.

Elliptic curve

By modularity this newform is the one attached to the isogeny class 256.a (Cremona's 256a). Its optimal curve 256a1 is

$y^2 = x^3 + x^2 - 3x + 1$

of rank 1 with torsion of order 2. Its $a_p$, computed by Sagebrush's point-counting engine, equal the newform's for every prime $p < 1000$.

Traces of Hecke eigenvalues

$\operatorname{tr} a_n$ for every $n \le 1000$ is in the JSON.

Sato–Tate

With CM the normalized $a_p / 2p^{1/2}$ for the primes $p < 1000$ not dividing 256, against the semicircle $\tfrac{2}{\pi}\sqrt{1 - x^2}$ (CM forms follow a different law):

Provenance

Stored in the atlas: computed by Sagebrush's modular symbols engine in 0.192 s (one thread) and proven: the dimensions are certified, and the characteristic polynomial of $T$ over $\mathbb{Z}$ is reconstructed by CRT past a rigorous coefficient bound. The label, dimension and $\operatorname{tr} a_p$ for every $p < 1000$ equal LMFDB's.

newform_orbits(256, 2)[0]   # 256.2.a.a

cargo run --release -p sagebrush-web --example atlas -- 256:2 1000