Atlas › Modular forms › Weight 2 › Level 91 › 91.2.a

Newspace 91.2.a: $S_{2}^{\mathrm{new}}(\Gamma_0(91))$

Newforms

Label	Dim	Coefficient field	Trace form	AL signs	Sign	Elliptic curve
91.2.a.a	1	$\mathbb{Q}$	$q - 2q^{2} + 2q^{4} - 3q^{5} - q^{7} + O(q^{8})$	+ +	$-1$	91a1 rank 1
91.2.a.b	1	$\mathbb{Q}$	$q - 2q^{3} - 2q^{4} - 3q^{5} + q^{7} + O(q^{8})$	− −	$-1$	91b1 rank 1
91.2.a.c	2	$\mathbb{Q}(\sqrt{2})$	$2q + 6q^{5} - 4q^{6} + 2q^{7} + O(q^{8})$	− +	$+1$
91.2.a.d	3	degree 3	$3q + q^{2} - 2q^{3} + 3q^{4} + 2q^{5} + 4q^{6} - 3q^{7} + O(q^{8})$	+ −	$+1$

Hecke characteristic polynomials

The eigenvalue of $T = T_{2} + 3T_{3}$ generates each orbit's coefficient field; on the newspace its characteristic polynomial factors over $\mathbb{Q}$ as one irreducible factor per orbit:

Orbit	Characteristic polynomial of $T$
91.2.a.a	$x + 2$
91.2.a.b	$x + 6$
91.2.a.c	$x^{2} - 8$
91.2.a.d	$x^{3} + 5x^{2} - 76x - 88$

Dimensions

Newforms $S_{2}^{\mathrm{new}}(\Gamma_0(91))$	7
Old forms	0
Cusp forms $S_{2}(\Gamma_0(91))$	7
Eisenstein series $E_{2}(\Gamma_0(91))$	3
Modular forms $M_{2}(\Gamma_0(91))$	10

Decomposition of the old subspace

The old subspace is 0.

Provenance

Stored in the atlas: computed by Sagebrush's modular symbols engine in 0.249 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 engine's checks

dim M^+ at levels [1, 7, 13, 91]: [0, 1, 1, 10] (certified at ell = 2147483629)
T = [(2, 1), (3, 3)]; h of degree 7 = 1 x 7 (phi(ord eps) x dim S_k^new); 1 primes, 0 rejected

Open in the notebook · JSON · stored data

Recompute it yourself

In Sage mode at sagebrush.space (or npx sagebrush --sage):

newform_orbits(91, 2)

With the Rust engine (source), in engine/:

cargo run --release -p sagebrush-web --example atlas -- 91:2 1000

← 90.2.a · 92.2.a →