O.g.f.: (1 + 4*x)/((1 + x)*sqrt(1 - 8*x)).

Terms

a(0) =1a(1) =7a(2) =33a(3) =223a(4) =1537a(5) =11007a(6) =80385a(7) =595455a(8) =4456449a(9) =33615871a(10) =255148033a(11) =1946337279a(12) =14908784641a(13) =114597822463a(14) =883479412737