Theta series of A_20 lattice.

Terms

a(0) =1a(1) =420a(2) =35910a(3) =1093260a(4) =15058680a(5) =113446872a(6) =579316080a(7) =2329395060a(8) =7731638460a(9) =22367855300a(10) =57613059966a(11) =136098325440a(12) =297252637920a(13) =612084784920