a(n) = floor(11^n/9^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =3a(7) =4a(8) =4a(9) =6a(10) =7a(11) =9a(12) =11a(13) =13a(14) =16a(15) =20a(16) =24a(17) =30a(18) =37a(19) =45a(20) =55a(21) =67a(22) =82a(23) =101a(24) =123a(25) =150a(26) =184a(27) =225a(28) =275a(29) =336