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%I #16 Sep 08 2022 08:46:12
%S 1,0,6,0,12,12,6,24,18,0,24,12,12,24,66,12,48,36,6,24,60,24,60,36,18,
%T 48,60,0,156,48,24,48,102,12,72,132,12,48,96,24,144,60,66,72,132,12,
%U 108,72,48,168,138,36,144,72,6,120,342,24,132,72,60,96,144,24
%N Theta series of 4-dimensional 21-modular lattice A2xT7 with minimal norm 4.
%H G. Nebe and N. J. A. Sloane, <a href="http://www.math.rwth-aachen.de/~Gabriele.Nebe/LATTICES/21moddim4.html">Home page for this lattice</a>
%e G.f. = 1 + 6*x^2 + 12*x^4 + 12*x^5 + 6*x^6 + 24*x^7 + 18*x^8 + 24*x^10 + ...
%e G.f. = 1 + 6*q^4 + 12*q^8 + 12*q^10 + 6*q^12 + 24*q^14 + 18*q^16 + 24*q^20 + ...
%o (PARI) {a(n) = if( n<0, 0, polcoeff( 1 + 2 * x * Ser( qfrep( [4, 2, 2, 1; 2, 4, 1, 2; 2, 1, 8, 4; 1, 2, 4, 8], n, 1)), n))};
%o (Magma) A := Basis( ModularForms( Gamma0(21), 2), 64); A[1] + 6*A[3];
%K nonn
%O 0,3
%A _Michael Somos_, Apr 12 2015
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