a(n) = A220437(n)/2.

Terms

a(0) =3a(1) =14a(2) =170a(3) =1152a(4) =10326a(5) =78963a(6) =656624a(7) =5213426a(8) =42439104a(9) =340790424a(10) =2756911059a(11) =22212987398a(12) =179367321962