a(n) = number of n-digit base-3 biquams.

Terms

a(0) =0a(1) =2a(2) =7a(3) =23a(4) =73a(5) =227a(6) =697a(7) =2123a(8) =6433a(9) =19427a(10) =58537a(11) =176123a(12) =529393a(13) =1590227a(14) =4774777a(15) =14332523a(16) =43013953a(17) =129074627a(18) =387289417a(19) =1161999323a(20) =3486260113a(21) =10459304627a(22) =31378962457a(23) =94138984523a(24) =282421147873a(25) =847271832227