a(n) = 4*a(n-1) + 8*a(n-2), with a(1)=0 and a(2)=1.

Terms

a(0) =0a(1) =1a(2) =4a(3) =24a(4) =128a(5) =704a(6) =3840a(7) =20992a(8) =114688a(9) =626688a(10) =3424256a(11) =18710528a(12) =102236160a(13) =558628864a(14) =3052404736a(15) =16678649856a(16) =91133837312a(17) =497964548096