Number of permutations of [n] with exactly 4 descents which avoid the pattern 1324.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =57a(6) =812a(7) =6524a(8) =37309a(9) =169298a(10) =648216a(11) =2176923a(12) =6582869a(13) =18262399a(14) =47129249a(15) =114344261a(16) =262987603a(17) =577216181a(18) =1215552037a(19) =2467076907a(20) =4843870146a(21) =9229556242a(22) =17113017451a(23) =30949065535a(24) =54705281270a(25) =94677736245a(26) =160689668475a(27) =267828562140a(28) =438931138500