

A300781


Number of logconcave permutations of {1,...,n}.


1



1, 1, 2, 4, 8, 10, 14, 18, 22, 18, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12
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OFFSET

0,3


COMMENTS

a(n) = 12 for n >= 10, since for these n the only logconcave permutations of {1,...,n} are (1,2,...,n), (1,2,4,5,...,n,3), (1,2,4,6,...,7,5,3), (1,3,4,...,n,2), (1,3,5,...,6,4,2), (1,n,...,3,2), and the reverses of these.


LINKS

Table of n, a(n) for n=0..78.
Pontus Andersson (von Brömssen), Logconcave permutations, Manuscript, 2002.
MathWorld, Logarithmically Concave Sequence.
Index entries for linear recurrences with constant coefficients, signature (1).


FORMULA

G.f.: (6*x^10 +4*x^9 4*x^8 4*x^7 4*x^6 2*x^5 4*x^4 2*x^3 x^2 1)/(x1).


CROSSREFS

Cf. A069916, A301454.
Sequence in context: A189670 A341822 A034822 * A050567 A069879 A074330
Adjacent sequences: A300778 A300779 A300780 * A300782 A300783 A300784


KEYWORD

easy,nonn


AUTHOR

Pontus von Brömssen, Mar 12 2018


STATUS

approved



