G.f. A(x) satisfies: A(x) = (1 - x) / (1 - 2 * x - x^2 - x^2 * A(x)).

Terms

a(0) =1a(1) =1a(2) =4a(3) =11a(4) =35a(5) =111a(6) =365a(7) =1221a(8) =4160a(9) =14371a(10) =50251a(11) =177503a(12) =632514a(13) =2271027a(14) =8208259a(15) =29840993a(16) =109049568a(17) =400352639a(18) =1475929092a(19) =5461571729a(20) =20279092033a(21) =75531360153a(22) =282123848574