Number of compositions of n such that the minimal distance between two identical parts equals two.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =2a(6) =3a(7) =8a(8) =16a(9) =34a(10) =57a(11) =113a(12) =213a(13) =396a(14) =733a(15) =1333a(16) =2419a(17) =4400a(18) =7934a(19) =14321a(20) =25687a(21) =45947a(22) =82085a(23) =146410a(24) =260547a(25) =463021a(26) =821669a(27) =1456296a(28) =2578051a(29) =4559972