Theta series of direct sum of 2 copies of hexagonal lattice.

Terms

a(0) =1a(1) =12a(2) =36a(3) =12a(4) =84a(5) =72a(6) =36a(7) =96a(8) =180a(9) =12a(10) =216a(11) =144a(12) =84a(13) =168a(14) =288a(15) =72a(16) =372a(17) =216a(18) =36a(19) =240a(20) =504a(21) =96a(22) =432a(23) =288a(24) =180a(25) =372a(26) =504a(27) =12a(28) =672a(29) =360