floor(r*a(n-1)) + floor(r*a(n-2)), where r = 3/2, a(0) = 1, a(1) = 1.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =9a(5) =19a(6) =41a(7) =89a(8) =194a(9) =424a(10) =927a(11) =2026a(12) =4429a(13) =9682a(14) =21166a(15) =46272a(16) =101157a(17) =221143a(18) =483449a(19) =1056887a(20) =2310503a(21) =5051084a(22) =11042380a(23) =24140196a(24) =52773864a(25) =115371090a(26) =252217431a(27) =551382781a(28) =1205400317a(29) =2635174646