a(n+2) = 3*a(n) - a(n-2) with a(0) = 1, a(1) = 3, a(2) = 6.

Terms

a(0) =1a(1) =3a(2) =6a(3) =9a(4) =19a(5) =30a(6) =63a(7) =99a(8) =208a(9) =327a(10) =687a(11) =1080a(12) =2269a(13) =3567a(14) =7494a(15) =11781a(16) =24751a(17) =38910a(18) =81747a(19) =128511a(20) =269992a(21) =424443a(22) =891723a(23) =1401840a(24) =2945161a(25) =4629963a(26) =9727206a(27) =15291729a(28) =32126779a(29) =50505150