

A301454


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


2



1, 1, 2, 4, 6, 8, 10, 12, 12, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8
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OFFSET

0,3


COMMENTS

a(n) = 8 for n >= 9, since for these n the only strictly logconcave permutations of {1,...,n} are (1,2,...,n), (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..105.
Pontus Andersson (von Brömssen), Logconcave permutations, Manuscript, 2002.
Eric Weisstein's World of Mathematics, Logarithmically Concave Sequence


FORMULA

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


PROG

(PARI) Vec((4*x^9 2*x^7 2*x^6 2*x^5 2*x^4 2*x^3 x^2 1)/(x1) + O(x^100)) \\ Felix Fröhlich, Mar 23 2018


CROSSREFS

Cf. A300781.
Sequence in context: A241071 A319807 A055954 * A161602 A285591 A327210
Adjacent sequences: A301451 A301452 A301453 * A301455 A301456 A301457


KEYWORD

easy,nonn


AUTHOR

Pontus von Brömssen, Mar 21 2018


STATUS

approved



