A double product sequence based on a=3;f(n,a)=f(n-1,a)+a*f(n-2,a).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =4a(5) =1a(6) =1a(7) =28a(8) =28a(9) =1a(10) =1a(11) =133a(12) =931a(13) =133a(14) =1a(15) =1a(16) =760a(17) =25270a(18) =25270a(19) =760a(20) =1a(21) =1a(22) =3880a(23) =737200a(24) =3501700a(25) =737200a(26) =3880a(27) =1a(28) =1a(29) =21049