a(0)=1, a(1)=3, a(n) = 6*a(n-1) - 7*a(n-2), n >= 2.

Terms

a(0) =1a(1) =3a(2) =11a(3) =45a(4) =193a(5) =843a(6) =3707a(7) =16341a(8) =72097a(9) =318195a(10) =1404491a(11) =6199581a(12) =27366049a(13) =120799227a(14) =533233019a(15) =2353803525a(16) =10390190017a(17) =45864515427a(18) =202455762443a(19) =893682966669