G.f. = theta_4(0,x^4)/theta_4(0,x).

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =12a(5) =20a(6) =32a(7) =48a(8) =72a(9) =106a(10) =152a(11) =216a(12) =304a(13) =420a(14) =576a(15) =784a(16) =1056a(17) =1412a(18) =1876a(19) =2472a(20) =3240a(21) =4224a(22) =5472a(23) =7056a(24) =9056a(25) =11566a(26) =14712a(27) =18640a(28) =23520a(29) =29572