Number of compositions of n such that the set of parts is {1,2,3}.

Terms

a(0) =6a(1) =12a(2) =32a(3) =72a(4) =152a(5) =311a(6) =625a(7) =1225a(8) =2378a(9) =4566a(10) =8700a(11) =16475a(12) =31052a(13) =58290a(14) =109079a(15) =203584a(16) =379144a(17) =704821a(18) =1308268a(19) =2425259a(20) =4491074a(21) =8308879a(22) =15360082a(23) =28376089a(24) =52391492a(25) =96683649a(26) =178344205a(27) =328854566a(28) =606190627a(29) =1117103729