a(n) = A027011(2n, n+4).

Terms

a(0) =1a(1) =12a(2) =343a(3) =3864a(4) =26990a(5) =140455a(6) =599801a(7) =2228414a(8) =7486615a(9) =23370193a(10) =69141497a(11) =196766283a(12) =544680787a(13) =1478898009a(14) =3962865228a(15) =10526310127a(16) =27802386717a(17) =73170829088a(18) =192150938490a(19) =503938185601