Number of permutations of length n which avoid the patterns 1234, 4123, 4132.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =76a(5) =263a(6) =843a(7) =2501a(8) =6941a(9) =18245a(10) =45928a(11) =111721a(12) =264482a(13) =612707a(14) =1394929a(15) =3131269a(16) =6948043a(17) =15269985a(18) =33290710a(19) =72085673a(20) =155182152a(21) =332387343a(22) =708820807a(23) =1505731877a(24) =3187639497a(25) =6727621949a(26) =14159916404a(27) =29729158217