a(n) = floor(7^n/5^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =5a(6) =7a(7) =10a(8) =14a(9) =20a(10) =28a(11) =40a(12) =56a(13) =79a(14) =111a(15) =155a(16) =217a(17) =304a(18) =426a(19) =597a(20) =836a(21) =1171a(22) =1639a(23) =2295a(24) =3214a(25) =4499a(26) =6299a(27) =8819a(28) =12347a(29) =17286