Number of subsets of {1,2,...,n} such that no two elements differ by 1, 4, or 5.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =8a(5) =11a(6) =14a(7) =19a(8) =25a(9) =34a(10) =49a(11) =70a(12) =99a(13) =141a(14) =196a(15) =270a(16) =375a(17) =520a(18) =723a(19) =1014a(20) =1420a(21) =1985a(22) =2777a(23) =3874a(24) =5396a(25) =7526a(26) =10496a(27) =14642a(28) =20449a(29) =28555