a(n) = 4*a(n-1) + 6*a(n-2), a(0)=1, a(1)=2.

Terms

a(0) =1a(1) =2a(2) =14a(3) =68a(4) =356a(5) =1832a(6) =9464a(7) =48848a(8) =252176a(9) =1301792a(10) =6720224a(11) =34691648a(12) =179087936a(13) =924501632a(14) =4772534144a(15) =24637146368a(16) =127183790336a(17) =656558039552