Triangle read by rows: T(n,k) = Sum_{j=0..k} (-1)^j * binomial(k,j) * (3-j)^n.

Terms

a(0) =1a(1) =3a(2) =1a(3) =9a(4) =5a(5) =2a(6) =27a(7) =19a(8) =12a(9) =6a(10) =81a(11) =65a(12) =50a(13) =36a(14) =24a(15) =243a(16) =211a(17) =180a(18) =150a(19) =120a(20) =120a(21) =729a(22) =665a(23) =602a(24) =540a(25) =480a(26) =360a(27) =720a(28) =2187a(29) =2059