a(n) = 7 + floor((1 + Sum_{j=1..n-1} a(j))/4).

Terms

a(0) =7a(1) =9a(2) =11a(3) =14a(4) =17a(5) =21a(6) =27a(7) =33a(8) =42a(9) =52a(10) =65a(11) =81a(12) =102a(13) =127a(14) =159a(15) =199a(16) =248a(17) =310a(18) =388a(19) =485a(20) =606a(21) =758a(22) =947a(23) =1184a(24) =1480a(25) =1850a(26) =2312a(27) =2890a(28) =3613a(29) =4516