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A177283 Number of permutations of 2 copies of 1..n with all adjacent differences <= 2 in absolute value. 0
1, 1, 6, 90, 660, 3846, 24326, 148146, 850920, 4788114, 26548704, 144707622, 778116870, 4140736398, 21836757474, 114262071558 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) = (2n)!/2^n for n<=3.

LINKS

Table of n, a(n) for n=0..15.

CROSSREFS

Cf. A000680.

Sequence in context: A166782 A121249 A113404 * A121607 A100594 A002432

Adjacent sequences:  A177280 A177281 A177282 * A177284 A177285 A177286

KEYWORD

nonn

AUTHOR

R. H. Hardin, May 06 2010

STATUS

approved

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Last modified January 17 18:02 EST 2020. Contains 330987 sequences. (Running on oeis4.)