G.f.: (1-5*x+3*x^2+x^3)/(1-7*x+10*x^2+x^3-x^4).

Terms

a(0) =1a(1) =2a(2) =7a(3) =29a(4) =132a(5) =629a(6) =3061a(7) =15034a(8) =74131a(9) =366145a(10) =1809732a(11) =8947577a(12) =44243705a(13) =218786578a(14) =1081931151a(15) =5350356149a(16) =26458638660a(17) =130843764557a(18) =647051540301