Number of compositions of n that avoid the pattern 23-1.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =16a(6) =31a(7) =61a(8) =118a(9) =228a(10) =440a(11) =846a(12) =1623a(13) =3111a(14) =5955a(15) =11385a(16) =21752a(17) =41530a(18) =79250a(19) =151161a(20) =288224a(21) =549408a(22) =1047034a(23) =1995000a(24) =3800662a(25) =7239710a(26) =13789219a(27) =26261678a(28) =50012275a(29) =95237360