E.g.f.: x/(1-x)+log((1-x)/(1-2*x)).

Terms

a(0) =0a(1) =2a(2) =5a(3) =20a(4) =114a(5) =864a(6) =8280a(7) =96480a(8) =1325520a(9) =20966400a(10) =374855040a(11) =7468070400a(12) =163938297600