Subsets of {1,2,...,n-6} without differences equal to 3 or 6.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =2a(8) =4a(9) =8a(10) =12a(11) =18a(12) =27a(13) =36a(14) =48a(15) =64a(16) =96a(17) =144a(18) =216a(19) =324a(20) =486a(21) =729a(22) =1053a(23) =1521a(24) =2197a(25) =3211a(26) =4693a(27) =6859a(28) =10108a(29) =14896