G.f.: Product_{k>=1} (1 + 2*x^k).

Terms

a(0) =1a(1) =2a(2) =2a(3) =6a(4) =6a(5) =10a(6) =18a(7) =22a(8) =30a(9) =42a(10) =66a(11) =78a(12) =110a(13) =138a(14) =186a(15) =254a(16) =318a(17) =402a(18) =522a(19) =654a(20) =822a(21) =1074a(22) =1306a(23) =1638a(24) =2022a(25) =2514a(26) =3058a(27) =3798a(28) =4662a(29) =5658