Not of form (x^2+xy+2y^2 with x >= 0, y >= 0).

Terms

a(0) =3a(1) =5a(2) =6a(3) =7a(4) =10a(5) =12a(6) =13a(7) =15a(8) =17a(9) =19a(10) =20a(11) =21a(12) =24a(13) =26a(14) =27a(15) =29a(16) =30a(17) =31a(18) =33a(19) =34a(20) =35a(21) =38a(22) =39a(23) =40a(24) =41a(25) =42a(26) =45a(27) =47a(28) =48a(29) =51