Expansion of (theta_3(z)*theta_3(21z)+theta_2(z)*theta_2(21z))^2.

Terms

a(0) =1a(1) =0a(2) =4a(3) =0a(4) =4a(5) =0a(6) =0a(7) =0a(8) =4a(9) =0a(10) =8a(11) =8a(12) =0a(13) =16a(14) =0a(15) =8a(16) =4a(17) =16a(18) =4a(19) =16a(20) =8a(21) =0a(22) =16a(23) =24a(24) =0a(25) =16a(26) =40a(27) =0a(28) =0a(29) =16