Number of permutations of length n which avoid the patterns 2143, 1324 (smooth permutations); or avoid the patterns 1342, 2431; etc.

A032351

Number of permutations of length n which avoid the patterns 2143, 1324 (smooth permutations); or avoid the patterns 1342, 2431; etc.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =6a(4) =22a(5) =88a(6) =366a(7) =1552a(8) =6652a(9) =28696a(10) =124310a(11) =540040a(12) =2350820a(13) =10248248a(14) =44725516a(15) =195354368a(16) =853829272a(17) =3733693872a(18) =16333556838a(19) =71476391800a(20) =312865382004

External references