Number of permutations of length n which avoid the patterns 321, 2341, 4123.

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =26a(5) =58a(6) =131a(7) =295a(8) =662a(9) =1487a(10) =3342a(11) =7510a(12) =16874a(13) =37915a(14) =85195a(15) =191432a(16) =430143a(17) =966522a(18) =2171756a(19) =4879892a(20) =10965017a(21) =24638169a(22) =55361464a(23) =124396081a(24) =279515456a(25) =628065528a(26) =1411250432a(27) =3171050937a(28) =7125286777a(29) =16010374058