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

Terms

a(0) =-1a(1) =-1a(2) =0a(3) =2a(4) =9a(5) =30a(6) =95a(7) =299a(8) =955a(9) =3113a(10) =10360a(11) =35131a(12) =121073a(13) =423002a(14) =1494987a(15) =5335329a(16) =19199601a(17) =69587445a(18) =253789506a(19) =930660441a(20) =3429351837a(21) =12691395888a(22) =47151135165a(23) =175791361713a(24) =657484674168