Triangle read by rows: T(n,k) = 3^(n-k)*C(2*n,n-k).

Terms

a(0) =1a(1) =6a(2) =1a(3) =54a(4) =12a(5) =1a(6) =540a(7) =135a(8) =18a(9) =1a(10) =5670a(11) =1512a(12) =252a(13) =24a(14) =1a(15) =61236a(16) =17010a(17) =3240a(18) =405a(19) =30a(20) =1a(21) =673596a(22) =192456a(23) =40095a(24) =5940a(25) =594a(26) =36a(27) =1a(28) =7505784a(29) =2189187