A107497 Theta series of quadratic form with Gram matrix [ 2, 1, 1, 1; 1, 20, 7, 7; 1, 7, 20, 7; 1, 7, 7, 46].

1, 2, 0, 0, 2, 0, 0, 0, 0, 2, 8, 0, 8, 2, 4, 0, 10, 4, 0, 0, 0, 0, 12, 4, 0, 6, 6, 12, 0, 8, 20, 0, 0, 0, 0, 16, 22, 0, 24, 8, 24, 0, 32, 20, 0, 0, 0, 0, 36, 14, 0, 20, 14, 16, 0, 24, 32, 0, 0, 0, 0, 20, 28, 0, 30, 12, 44, 0, 24, 24, 0, 0, 0, 0, 28, 44, 0, 32

Offset: 0

Author

N. J. A. Sloane, May 28 2005

Keywords

• nonn

Comments

G.f. is theta_1 in the Parry 1979 reference on page 166. This theta series is an element of the space of modular forms on Gamma_0(169) of weight 2 and dimension 21. - Andy Huchala, May 13 2023

Examples

			G.f. = 1 + 2*q^2 + 2*q^8 + 2*q^18 + ...
		

Links

• Andy Huchala, Table of n, a(n) for n = 0..20000
• W. R. Parry, A negative result on the representation of modular forms by theta series, J. Reine Angew. Math., 310 (1979), 151-170.

Crossrefs

Cf. A107498-A107505, A140686.

Programs

Magma

prec := 60;
ls := [[2,1,1,1],[1,20,7,7],[1,7,20,7],[1,7,7,46]];
S := Matrix(ls);
L := LatticeWithGram(S);
M := ThetaSeriesModularFormSpace(L);
B := Basis(M, prec);
T := ThetaSeries(L,44);
coeffs := [Coefficients(T)[2*i-1] : i in [1..23]];
Coefficients(&+[coeffs[i]*B[i] :i in [1..13]]+&+[coeffs[i+1]*B[i] :i in [14..19]] + coeffs[22]*B[20] + coeffs[23]*B[21]); // Andy Huchala, May 13 2023

Extensions

Name clarified and more terms from Andy Huchala, May 13 2023