Number of subsets of {1, 2, ..., n} that do not contain a subset of the form {x, 2x, 3x}.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =14a(5) =28a(6) =50a(7) =100a(8) =200a(9) =360a(10) =720a(11) =1440a(12) =2560a(13) =5120a(14) =10240a(15) =17920a(16) =35840a(17) =71680a(18) =130816a(19) =261632a(20) =523264a(21) =915712a(22) =1831424a(23) =3662848a(24) =6516608a(25) =13033216a(26) =26066432a(27) =46688768a(28) =93377536a(29) =186755072