a(n) = 6*a(n-1) - 6*a(n-2).

Terms

a(0) =1a(1) =5a(2) =24a(3) =114a(4) =540a(5) =2556a(6) =12096a(7) =57240a(8) =270864a(9) =1281744a(10) =6065280a(11) =28701216a(12) =135815616a(13) =642686400a(14) =3041224704a(15) =14391229824a(16) =68100030720a(17) =322252805376