a(n) = floor(9^n/7^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =3a(6) =4a(7) =5a(8) =7a(9) =9a(10) =12a(11) =15a(12) =20a(13) =26a(14) =33a(15) =43a(16) =55a(17) =71a(18) =92a(19) =118a(20) =152a(21) =195a(22) =251a(23) =323a(24) =416a(25) =535a(26) =688a(27) =884a(28) =1137a(29) =1462