T(2n,n+2), T given by A026747.

Terms

a(0) =1a(1) =7a(2) =37a(3) =178a(4) =823a(5) =3737a(6) =16833a(7) =75608a(8) =339610a(9) =1527944a(10) =6892210a(11) =31186533a(12) =141598200a(13) =645186895a(14) =2950261555a(15) =13538266219a(16) =62338173865a(17) =287993085103