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A117514 Number of ways of arranging 2n tokens in a row, with 2 copies of each token from 1 through n, such that the first token is a 1 and between every pair of tokens labeled i (i=1..n) there is exactly one taken labeled (i+1 mod n). 3
1, 1, 2, 18, 248, 5560, 174752 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..7.

CROSSREFS

Cf. A002105, A117513, A117515.

Sequence in context: A052635 A259270 A168562 * A138437 A265452 A121429

Adjacent sequences:  A117511 A117512 A117513 * A117515 A117516 A117517

KEYWORD

nonn

AUTHOR

Nan Zang (nzang(AT)cs.ucsd.edu), Apr 28 2006

STATUS

approved

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Last modified February 21 22:56 EST 2018. Contains 299427 sequences. (Running on oeis4.)