a(n) = 3*a(n-1) + 2*a(n-2) - 6*a(n-3).

Terms

a(0) =1a(1) =3a(2) =11a(3) =33a(4) =103a(5) =309a(6) =935a(7) =2805a(8) =8431a(9) =25293a(10) =75911a(11) =227733a(12) =683263a(13) =2049789a(14) =6149495a(15) =18448485a(16) =55345711a(17) =166037133a(18) =498111911a(19) =1494335733a(20) =4483008223a(21) =13449024669a(22) =40347076055a(23) =121041228165a(24) =363123688591