a(n) = 17 + floor( (1 + Sum_{j=0..n-1} a(j))/2 ).

Terms

a(0) =17a(1) =26a(2) =39a(3) =58a(4) =87a(5) =131a(6) =196a(7) =294a(8) =441a(9) =662a(10) =993a(11) =1489a(12) =2234a(13) =3351a(14) =5026a(15) =7539a(16) =11309a(17) =16963a(18) =25445a(19) =38167a(20) =57251a(21) =85876a(22) =128814a(23) =193221a(24) =289832a(25) =434748a(26) =652122a(27) =978183a(28) =1467274a(29) =2200911