a(n) = 19 + floor( Sum_{j=1..n-1} a(j) / 2 ).

Terms

a(0) =19a(1) =28a(2) =42a(3) =63a(4) =95a(5) =142a(6) =213a(7) =320a(8) =480a(9) =720a(10) =1080a(11) =1620a(12) =2430a(13) =3645a(14) =5467a(15) =8201a(16) =12301a(17) =18452a(18) =27678a(19) =41517a(20) =62275a(21) =93413a(22) =140119a(23) =210179a(24) =315268a(25) =472902a(26) =709353a(27) =1064030a(28) =1596045a(29) =2394067