T(2n,n-2), T given by A026703.

Terms

a(0) =1a(1) =8a(2) =48a(3) =261a(4) =1358a(5) =6907a(6) =34683a(7) =172827a(8) =857077a(9) =4237179a(10) =20904293a(11) =102987450a(12) =506887889a(13) =2493127016a(14) =12256531946a(15) =60233878032a(16) =295941325816