a(n) = (4*3^n + (-7)^n)/5.

Terms

a(0) =1a(1) =1a(2) =17a(3) =-47a(4) =545a(5) =-3167a(6) =24113a(7) =-162959a(8) =1158209a(9) =-8054975a(10) =56542289a(11) =-395323631a(12) =2768682593a(13) =-19376526623a(14) =135648440945a(15) =-949500822863