a(n) = 13 + floor(Sum_{j=1..n-1} a(j)/2).

Terms

a(0) =13a(1) =19a(2) =29a(3) =43a(4) =65a(5) =97a(6) =146a(7) =219a(8) =328a(9) =492a(10) =738a(11) =1107a(12) =1661a(13) =2491a(14) =3737a(15) =5605a(16) =8408a(17) =12612a(18) =18918a(19) =28377a(20) =42565a(21) =63848a(22) =95772a(23) =143658a(24) =215487a(25) =323230a(26) =484845a(27) =727268a(28) =1090902a(29) =1636353