A029821 - OEIS

%I #7 Jul 08 2025 19:21:49

%S 31,8,4104,157472,2093064,15625008,80783136,322828864,1071640584,

%T 3099521384,8015629104,18863581536,41199871776,84835994992,

%U 165611207232,307562657472,548679970824,948703011984,1590054469992,2581501582240

%N Average theta series of odd unimodular lattices of dimension 20 (multiplied by 31).

%o (PARI) a(n)=if(n<1,31*(n==0),8*(sigma(n,9)-if(n%4==0,1024*sigma(n/4,9)))) /* _Michael Somos_, Jul 16 2004 */

%K nonn

%O 0,1

%A _N. J. A. Sloane_