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).

1, 1, 2, 18, 248, 5560, 174752

Offset

1,3

Links

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

Crossrefs

Cf. A002105, A117513, A117515.

Sequence in context: A366001 A259270 A168562 * A138437 A265452 A379253

Adjacent sequences: A117511 A117512 A117513 * A117515 A117516 A117517

Keyword

nonn

Author

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

Status

approved