T(n, 2n-9), T given by A027960.

Terms

a(0) =3a(1) =7a(2) =18a(3) =47a(4) =123a(5) =319a(6) =806a(7) =1954a(8) =4506a(9) =9859a(10) =20495a(11) =40615a(12) =77040a(13) =140455a(14) =247085a(15) =420906a(16) =696509a(17) =1122751a(18) =1767344a(19) =2722551a(20) =4112177a(21) =6100063a(22) =8900312a(23) =12789498a(24) =18121132a(25) =25342683a(26) =35015477a(27) =47837823a(28) =64671742