Triangle U, read by rows, where U(n,k) = Product_{j=k..n-1} (3*j+1) for n > k with U(n,n) = 1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =4a(5) =1a(6) =28a(7) =28a(8) =7a(9) =1a(10) =280a(11) =280a(12) =70a(13) =10a(14) =1a(15) =3640a(16) =3640a(17) =910a(18) =130a(19) =13a(20) =1a(21) =58240a(22) =58240a(23) =14560a(24) =2080a(25) =208a(26) =16a(27) =1a(28) =1106560a(29) =1106560