Number of permutations of length n which avoid the patterns 1234, 1243, 2431.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =75a(5) =256a(6) =826a(7) =2535a(8) =7474a(9) =21370a(10) =59718a(11) =164082a(12) =445266a(13) =1197326a(14) =3198035a(15) =8499466a(16) =22505676a(17) =59427975a(18) =156598649a(19) =412008060a(20) =1082704623a(21) =2842662437a(22) =7458393801a(23) =19558738331a(24) =51270256195a(25) =134356895501