Number of subsets of {1..n} containing n but not containing all first differences.

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =4a(5) =12a(6) =23a(7) =53a(8) =104a(9) =218a(10) =437a(11) =893a(12) =1785a(13) =3620a(14) =7264a(15) =14634a(16) =29382a(17) =59097a(18) =118617a(19) =238291a(20) =478191a(21) =959867a(22) =1925681a(23) =3863365a(24) =7748136a(25) =15538461a(26) =31154278a(27) =62458007a(28) =125194936a(29) =250924636