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A087923 Number of ways of arranging the numbers 1 ... 2n into a 2 X n array so there is exactly one local maximum. 2
2, 16, 208, 3584, 76544, 1947648, 57477120, 1929117696, 72545402880, 3020819005440, 137959904378880, 6855868809216000, 368270708268072960, 21262037565623500800, 1312956239068318924800, 86347473137975269785600, 6025205587810776514560000, 444600907757468888806195200 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..200

FORMULA

a(n) = 2*Sum_{k=1..n} (2*n-2)!*(2*k*(n-k+1)-1)/((2*k-1)!!*(2*n-2*k-1)!!). - Maximilian Göbel, Feb 26 2020

PROG

(PARI) a(n)={2*sum(k=1, n, (2*n-2)!*(2*k*(n-k+1)-1)*2^n*k!*(n-k)!/((2*k)!*(2*n-2*k)!))} \\ Andrew Howroyd, Feb 26 2020

CROSSREFS

Row 2 of A087783.

Cf. A007846.

Sequence in context: A303673 A161568 A138429 * A222523 A004121 A188600

Adjacent sequences:  A087920 A087921 A087922 * A087924 A087925 A087926

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 27 2003

EXTENSIONS

Terms a(16) and beyond from Andrew Howroyd, Feb 26 2020

STATUS

approved

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Last modified July 10 14:17 EDT 2020. Contains 335576 sequences. (Running on oeis4.)