a(n) = (1/2)*A289787(n).

Terms

a(0) =1a(1) =6a(2) =31a(3) =156a(4) =785a(5) =3954a(6) =19919a(7) =100344a(8) =505489a(9) =2546430a(10) =12827791a(11) =64620756a(12) =325530881a(13) =1639881066a(14) =8260997855a(15) =41615265264a(16) =209639359969