Number of subsets of {1,2,...,n} such that no two elements differ by 2 or 5.

Terms

a(0) =1a(1) =2a(2) =4a(3) =6a(4) =9a(5) =15a(6) =21a(7) =29a(8) =45a(9) =69a(10) =100a(11) =152a(12) =236a(13) =349a(14) =517a(15) =789a(16) =1185a(17) =1757a(18) =2653a(19) =4014a(20) =5992a(21) =8986a(22) =13573a(23) =20363a(24) =30485a(25) =45901a(26) =69041a(27) =103481a(28) =155468a(29) =233908