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A258683 Total number of permutations on {1,2,...,n} that have a unique longest increasing subsequence and a unique longest decreasing subsequence. 1
1, 0, 0, 0, 2, 16, 120, 938, 8014, 74060, 748628, 8163156, 96429784 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,5
COMMENTS
By definition, a(n) <= A167995(n).
LINKS
Manfred Scheucher, C Code
EXAMPLE
the two permutation of {1,2,...,5}:
{2, 5, 3, 1, 4}
{4, 1, 3, 5, 2}
8 of the 16 permutations of {1,2,...,6} (others reversed):
{1, 3, 6, 4, 2, 5}
{1, 5, 2, 4, 6, 3}
{2, 3, 6, 4, 1, 5}
{2, 5, 3, 1, 4, 6}
{2, 6, 3, 1, 4, 5}
{2, 6, 5, 3, 1, 4}
{3, 6, 4, 2, 1, 5}
{3, 6, 4, 2, 5, 1}
PROG
(Sage)
def A258683(n):
return len([p for p in permutations(n) if len(p.longest_increasing_subsequences())* len(p.reverse().longest_increasing_subsequences())==1])
# Manfred Scheucher, Jun 07 2015
CROSSREFS
Sequence in context: A112710 A046105 A086854 * A026129 A026158 A025185
KEYWORD
nonn,more
AUTHOR
Manfred Scheucher, Jun 07 2015
STATUS
approved

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Last modified May 27 14:41 EDT 2024. Contains 372861 sequences. (Running on oeis4.)