a(1) = 1; a(n+1) = 1 + Sum_{d|n} a(n/d) * a(d).

Terms

a(0) =1a(1) =2a(2) =5a(3) =11a(4) =27a(5) =55a(6) =131a(7) =263a(8) =571a(9) =1168a(10) =2445a(11) =4891a(12) =10113a(13) =20227a(14) =40979a(15) =82229a(16) =165632a(17) =331265a(18) =665365a(19) =1330731a(20) =2666729a(21) =5334769a(22) =10679319a(23) =21358639a(24) =42740683a(25) =85482096a(26) =171004645a(27) =342015001a(28) =684113793a(29) =1368227587