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

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =4a(5) =6a(6) =13a(7) =19a(8) =41a(9) =54a(10) =110a(11) =157a(12) =277a(13) =394a(14) =706a(15) =970a(16) =1691a(17) =2376a(18) =3905a(19) =5494a(20) =9130a(21) =12355a(22) =20262a(23) =28146a(24) =44316a(25) =61761a(26) =98023a(27) =132891a(28) =207912a(29) =285667