A268536 The number of permutations of {1,2,...,n,1,2,...,n} with the property that there are k numbers between the two k's in the set for k=1,...,n, as n runs through the positive integers congruent to -1 or 0 mod 4.

2, 2, 52, 300, 35584, 216288, 79619280, 653443600, 513629782560, 5272675722400, 7598911885030976, 93690316113031872, 223367222197529806464, 3214766521218764786304

Offset

1,1

Links

Table of n, a(n) for n=1..14.

Ali Assarpour, Amotz Bar-Noy, Ou Liuo, Counting the Number of Langford Skolem Pairings, arXiv:1507.00315 [cs.DM], 2015.

Crossrefs

This is A176127 without the zeros.

Sequence in context: A345463 A322106 A321693 * A323872 A037292 A239151

Adjacent sequences: A268533 A268534 A268535 * A268537 A268538 A268539

Keyword

nonn

Author

N. J. A. Sloane, Feb 22 2016

Status

approved