G.f.: (1-x)/(1-8*x-8*x^2+8*x^3).

Terms

a(0) =1a(1) =7a(2) =64a(3) =560a(4) =4936a(5) =43456a(6) =382656a(7) =3369408a(8) =29668864a(9) =261244928a(10) =2300355072a(11) =20255449088a(12) =178356473856