Expansion of g.f. -2*x/(1 - 5*x - sqrt(1-4*x) + x*sqrt(1-4*x) + 2*x^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =20a(5) =69a(6) =243a(7) =869a(8) =3145a(9) =11491a(10) =42312a(11) =156807a(12) =584288a(13) =2187298a(14) =8221257a(15) =31009841a(16) =117331070a(17) =445174418a(18) =1693270531a(19) =6454992143a(20) =24657428519a(21) =94363587324a(22) =361741068087