Number of subsets of {1, ..., n} that are neither double-free nor sum-free.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =2a(5) =6a(6) =21a(7) =49a(8) =119a(9) =266a(10) =626a(11) =1315a(12) =2859a(13) =5878a(14) =12798a(15) =26038a(16) =54485a(17) =109976a(18) =230159a(19) =462634a(20) =945846a(21) =1897597a(22) =3893242a(23) =7798862a(24) =15834340a(25) =31695551a(26) =64315161a(27) =128693477a(28) =259241944a(29) =518614045