T(2n,n+3), T given by A026758.

Terms

a(0) =1a(1) =8a(2) =46a(3) =233a(4) =1109a(5) =5102a(6) =23020a(7) =102718a(8) =455608a(9) =2015496a(10) =8912244a(11) =39452385a(12) =175026904a(13) =778762339a(14) =3476922430a(15) =15581908258a(16) =70108401416a(17) =316728595048