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

Terms

a(0) =0a(1) =1a(2) =3a(3) =9a(4) =21a(5) =46a(6) =92a(7) =180a(8) =330a(9) =595a(10) =1039a(11) =1793a(12) =3023a(13) =5030a(14) =8248a(15) =13388a(16) =21518a(17) =34231a(18) =54079a(19) =84607a(20) =131603a(21) =203050a(22) =311738a(23) =474974a(24) =720666a(25) =1086125a(26) =1629815a(27) =2431647a(28) =3612665a(29) =5339710