Number of subsets of {1,2,...,n} such that no two elements differ by 3 or 4.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =12a(5) =16a(6) =21a(7) =29a(8) =45a(9) =73a(10) =117a(11) =178a(12) =260a(13) =376a(14) =552a(15) =832a(16) =1273a(17) =1945a(18) =2937a(19) =4385a(20) =6521a(21) =9730a(22) =14612a(23) =22040a(24) =33252a(25) =50032a(26) =75053a(27) =112437a(28) =168549a(29) =253065