a(n) = floor((5/4)^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =3a(7) =4a(8) =5a(9) =7a(10) =9a(11) =11a(12) =14a(13) =18a(14) =22a(15) =28a(16) =35a(17) =44a(18) =55a(19) =69a(20) =86a(21) =108a(22) =135a(23) =169a(24) =211a(25) =264a(26) =330a(27) =413a(28) =516a(29) =646