T(n,3), array T as in A054090.

Terms

a(0) =3a(1) =8a(2) =26a(3) =108a(4) =554a(5) =3392a(6) =24138a(7) =195716a(8) =1781018a(9) =17974584a(10) =199254842a(11) =2406840668a(12) =31466482506a(13) =442700857328