Number of compositions of n having exactly four fixed points.

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =16a(5) =30a(6) =70a(7) =144a(8) =299a(9) =615a(10) =1261a(11) =2584a(12) =5238a(13) =10624a(14) =21482a(15) =43350a(16) =87331a(17) =175703a(18) =353074a(19) =708963a(20) =1422445a(21) =2852299a(22) =5716668a(23) =11453033a(24) =22938117a(25) =45928418a(26) =91941762a(27) =184021452a(28) =368267172a(29) =736898601