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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 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 December 16 19:11 EST 2018. Contains 318188 sequences. (Running on oeis4.)