a(n) = 2*a(n-1)+6*a(n-2) for n>=3, a(0)=1, a(1)=2, a(2)=8.

Terms

a(0) =1a(1) =2a(2) =8a(3) =28a(4) =104a(5) =376a(6) =1376a(7) =5008a(8) =18272a(9) =66592a(10) =242816a(11) =885184a(12) =3227264a(13) =11765632a(14) =42894848a(15) =156383488a(16) =570136064a(17) =2078573056a(18) =7577962496a(19) =27627363328a(20) =100722501632a(21) =367209183232