T(n,3), array T as in A054126.

Terms

a(0) =2a(1) =9a(2) =39a(3) =134a(4) =394a(5) =1040a(6) =2542a(7) =5876a(8) =13039a(9) =28080a(10) =59163a(11) =122694a(12) =251576a(13) =511720a(14) =1035068a(15) =2085640a(16) =4191629a(17) =8409592a(18) =16852833a(19) =33748170a(20) =67549470a(21) =135164720a(22) =270410170a(23) =540918620a(24) =1081955995a(25) =2164054496