Expansion of g.f.: ((1 - x - sqrt(1-6*x+5*x^2))/(2*x))^2.

Terms

a(0) =1a(1) =2a(2) =7a(3) =26a(4) =101a(5) =406a(6) =1676a(7) =7066a(8) =30302a(9) =131782a(10) =579867a(11) =2576982a(12) =11550237a(13) =52152330a(14) =237005385a(15) =1083211410a(16) =4975796735a(17) =22960105510a(18) =106377393365a(19) =494674698190