A249563 - OEIS

%I #26 Nov 24 2016 19:37:26

%S 1,1,2,4,9,22,57,156,447,1335,4140,13290,44055,150494,528860,1909010,

%T 7068879,26820161,104156616,413634176,1678323602,6952182325,

%U 29378908664,126568357635,555540596435,2482857618713,11292588202568,52241502972732,245700673227652,1174263543570678,5700387781450739

%N Number of length n permutations avoiding (132,{2},{}) and (123,{},{1}).

%C (132,{2},{}) is a vincular pattern. It has underlying classical pattern 132 and the extra requirement that the 3 and the 2 are adjacent in the permutation.

%C (123,{},{1}) is a co-vincular pattern. It has underlying classical pattern 123 and the extra requirement that the 1 and 2 are exactly one apart in the permutation.

%H Christian Bean, <a href="/A249563/a249563.txt">Sage code</a>

%H Christian Bean, A. Claesson, H. Ulfarsson, <a href="http://arxiv.org/abs/1512.03226">Simultaneous Avoidance of a Vincular and a Covincular Pattern of Length 3</a>, arXiv preprint arXiv:1512.03226, 2015

%F If x appears after x-1 then we say that x is a ceiling point.

%F aup(n,k,i,l) = sum( sum( adown(n-1,k,j,m) for m in [i+1..k] ) for j in [1..i] )

%F if i = 1 and l > i: adown(n,k,i,l) = aup(n-1,k,l,l) + sum( adown(n-1,k,j,l) for j in [i+1..k] ) + sum( a(n-1,k-1,j,l-1) for j in [1..k-1] )

%F if i = 1 and l <= 1: adown(n,k,i,l) = sum( adown(n-1,k,j,l) for j in [i+1..k] ) + sum( a(n-1,k-1,j,l-1) for j in [1..k-1] )

%F if i > 1 and l > i: adown = aup(n-1,k,l,l) + sum( adown(n-1,k,j,l) for j in [i+1..k] )

%F otherwise: adown(n,k,i,l) = sum( adown(n-1,k,j,l) for j in [i+1..k] )

%F a(n,k,i,l) = aup(n,k,i,l) + adown(n,k,i,l)

%F where n is the length, k is the number of left to right minima, i is the position of the maximum, l is the position of the first ceiling point where if l = 0 there is no ceiling point (notice positions are in relation the position of the left to right minima).

%F aup implies the maximum is a ceiling point and adown implies the maximum is not a ceiling point.

%F Initial Conditions: if k > n or i > k or i > l then aup(n,k,i,l) - adown(n,k,i,l) = 0, if i > l then aup(n,k,i,l) = 0, and finally aup(n,n-1,i,l) = 1.

%F a(n) = sum( sum( sum( a(n,k,j,m) for m in [1..k] ) for j in [1..k] ) for k in [1..n] )

%Y Cf. A249560, A249561, A249562.

%K nonn

%O 0,3

%A _Christian Bean_, Nov 01 2014