a(n) = floor(10^n/3^n).

Terms

a(0) =1a(1) =3a(2) =11a(3) =37a(4) =123a(5) =411a(6) =1371a(7) =4572a(8) =15241a(9) =50805a(10) =169350a(11) =564502a(12) =1881676a(13) =6272254a(14) =20907515a(15) =69691719a(16) =232305731a(17) =774352437a(18) =2581174791a(19) =8603915972a(20) =28679719907a(21) =95599066359a(22) =318663554532