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

Terms

a(0) =1a(1) =8a(2) =23a(3) =61a(4) =160a(5) =419a(6) =1097a(7) =2872a(8) =7519a(9) =19685a(10) =51536a(11) =134923a(12) =353233a(13) =924776a(14) =2421095a(15) =6338509a(16) =16594432a(17) =43444787a(18) =113739929a(19) =297775000a(20) =779585071a(21) =2040980213a(22) =5343355568a(23) =13989086491a(24) =36623903905a(25) =95882625224a(26) =251023971767a(27) =657189290077