a(n) = a(n-1)+floor(a(n-2)/4) with a(0)=3, a(1)=4.

Terms

a(0) =3a(1) =4a(2) =4a(3) =5a(4) =6a(5) =7a(6) =8a(7) =9a(8) =11a(9) =13a(10) =15a(11) =18a(12) =21a(13) =25a(14) =30a(15) =36a(16) =43a(17) =52a(18) =62a(19) =75a(20) =90a(21) =108a(22) =130a(23) =157a(24) =189a(25) =228a(26) =275a(27) =332a(28) =400a(29) =483