Number of subsets of {1..n} that contain n but do not form a finite arithmetic progression.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =7a(6) =21a(7) =49a(8) =111a(9) =235a(10) =488a(11) =996a(12) =2018a(13) =4060a(14) =8154a(15) =16342a(16) =32722a(17) =65485a(18) =131019a(19) =262085a(20) =524227a(21) =1048509a(22) =2097081a(23) =4194229a(24) =8388531a(25) =16777131a(26) =33554344a(27) =67108772a(28) =134217632a(29) =268435354