Expansion of g.f.: (1-2*x-sqrt(1-4*x+8*x^3-4*x^4))/(2*x^2*(1-x)).

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =19a(5) =51a(6) =143a(7) =407a(8) =1183a(9) =3487a(10) =10415a(11) =31439a(12) =95791a(13) =294191a(14) =909823a(15) =2830943a(16) =8856255a(17) =27839167a(18) =87888767a(19) =278545663a(20) =885903743a(21) =2826612095a(22) =9045147391a(23) =29022168063a(24) =93350430975a(25) =300949170431a(26) =972271227647