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A300781 Number of log-concave 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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) = 12 for n >= 10, since for these n the only log-concave 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), Log-concave permutations, Manuscript, 2002.

MathWorld, Logarithmically Concave Sequence.

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)/(x-1).

CROSSREFS

Cf. A069916, A301454.

Sequence in context: A290476 A189670 A034822 * A050567 A069879 A074330

Adjacent sequences:  A300778 A300779 A300780 * A300782 A300783 A300784

KEYWORD

easy,nonn

AUTHOR

Pontus von Brömssen, Mar 12 2018

STATUS

approved

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Last modified October 18 00:16 EDT 2018. Contains 316297 sequences. (Running on oeis4.)