Number of permutations of length n which avoid the patterns 1234, 3142, 4132.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =240a(6) =746a(7) =2217a(8) =6371a(9) =17864a(10) =49202a(11) =133759a(12) =360175a(13) =963044a(14) =2561604a(15) =6787167a(16) =17930815a(17) =47267250a(18) =124395032a(19) =326966211a(20) =858600521a(21) =2253029402a(22) =5908876016a(23) =15490375561a(24) =40595804773a(25) =106364147270a(26) =278630854386