a(0)=1, a(1)=3, a(n) = 8*a(n-1) - a(n-2).

Terms

a(0) =1a(1) =3a(2) =23a(3) =181a(4) =1425a(5) =11219a(6) =88327a(7) =695397a(8) =5474849a(9) =43103395a(10) =339352311a(11) =2671715093a(12) =21034368433a(13) =165603232371