G.f.: (1+x-2*x^2+2*x^3-sqrt(1-2*x-3*x^2+4*x^3-4*x^4))/(2*(1-x+x^2)).

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =7a(7) =14a(8) =33a(9) =73a(10) =174a(11) =407a(12) =987a(13) =2386a(14) =5877a(15) =14509a(16) =36210a(17) =90715a(18) =228863a(19) =579654a(20) =1475465a(21) =3768993a(22) =9664454a(23) =24857951a(24) =64133027a(25) =165900202a(26) =430242509a(27) =1118325365a(28) =2913106746a(29) =7603261427