a(n) = 6*a(n-1) - a(n-2), n >= 2, a(0)=1, a(1)=9.

Terms

a(0) =1a(1) =9a(2) =53a(3) =309a(4) =1801a(5) =10497a(6) =61181a(7) =356589a(8) =2078353a(9) =12113529a(10) =70602821a(11) =411503397a(12) =2398417561a(13) =13979001969a(14) =81475594253a(15) =474874563549