OFFSET
0,6
COMMENTS
Equivalently the maximal number of 1342, 2431, and 3124 patterns.
LINKS
M. H. Albert, M. D. Atkinson, C. C.Handley, D. A. Holton, and W. Stromquist, On packing densities of permutations, The Electronic Journal of Combinatorics, 9(1) (2002).
David Bevan, The permutation class Av(4213,2143), arXiv:1510.06328 [math.CO], 2015.
Rob Pratt, Greatest number of occurrences of the pattern 4213 in a permutation, Mathematics Stack Exchange.
Eric Weisstein's World of Mathematics, Permutation Pattern
EXAMPLE
For n = 7, a(7) = 13 because the permutation 7532146 has 13 instances of the pattern 4213, namely: 7536, 7526, 7516, 7546, 7324, 7326, 7314, 7316, 7214, 7216, 5324, 5314, and 5214.
Moreover, all other permutations in S_7 have 13 or fewer instances of this pattern.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Peter Kagey, Mar 20 2021
EXTENSIONS
a(10)-a(12) from Rob Pratt
a(13)-a(15) from Bert Dobbelaere, Mar 26 2021
STATUS
approved