a(n) = 6*a(n-1) - 3*a(n-2), a(0)=2, a(1)=13.

Terms

a(0) =2a(1) =13a(2) =72a(3) =393a(4) =2142a(5) =11673a(6) =63612a(7) =346653a(8) =1889082a(9) =10294533a(10) =56099952a(11) =305716113a(12) =1665996822a(13) =9078832593a(14) =49475005092a(15) =269613532773