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

Terms

a(0) =1a(1) =0a(2) =1a(3) =2a(4) =4a(5) =11a(6) =28a(7) =75a(8) =207a(9) =579a(10) =1647a(11) =4744a(12) =13807a(13) =40550a(14) =120016a(15) =357613a(16) =1071916a(17) =3229870a(18) =9777767a(19) =29724593a(20) =90705886a(21) =277744244a(22) =853123473a(23) =2627968236a(24) =8116487286a(25) =25128482223a(26) =77971354506a(27) =242439732171