Number of subsets of {1,2,...,n} such that no two elements differ by 1 or 6.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =8a(5) =13a(6) =21a(7) =29a(8) =45a(9) =66a(10) =99a(11) =148a(12) =218a(13) =337a(14) =497a(15) =755a(16) =1131a(17) =1699a(18) =2571a(19) =3824a(20) =5794a(21) =8661a(22) =13041a(23) =19601a(24) =29376a(25) =44311a(26) =66349a(27) =99936a(28) =150000a(29) =225387