T(2n,n+2), T given by A026769.

Terms

a(0) =1a(1) =6a(2) =29a(3) =132a(4) =591a(5) =2648a(6) =11970a(7) =54818a(8) =254868a(9) =1204042a(10) =5779861a(11) =28178306a(12) =139394333a(13) =698911166a(14) =3547422416a(15) =18204441884a(16) =94339586414a(17) =493148411592