Number of subsets of {1, ..., n} that are double-free but not sum-free.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =4a(6) =6a(7) =18a(8) =35a(9) =84a(10) =137a(11) =323a(12) =591a(13) =1313a(14) =2033a(15) =4360a(16) =7406a(17) =15581a(18) =23682a(19) =49184a(20) =84017a(21) =171744a(22) =259818a(23) =528784a(24) =853143a(25) =1727011a(26) =2601181a(27) =5243126a(28) =8784832a(29) =17662987