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A213270 Costas arrays such that the corresponding permutation is an involution. 4
1, 2, 2, 2, 4, 10, 20, 18, 20, 28, 36, 34, 50, 46, 62, 40, 38, 20, 12, 8, 16, 10, 20, 0, 4, 4, 14, 0, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Self-inverse permutations such that each row in the difference table consists of pairwise distinct elements (see example).

LINKS

Table of n, a(n) for n=1..29.

Scott Rickard, costasarrays.org (information and papers about Costas arrays).

EXAMPLE

The permutation (4, 7, 9, 1, 6, 5, 2, 8, 3) is an involution and corresponds to a Costas array:

   4  7  9  1  6  5  2  8  3  (Permutation: p(1), p(2), p(3), ..., p(n) )

   3  2 -8  5 -1 -3  6 -5     (step-1 differences: p(2)-p(1), p(3)-p(2), ... )

   5 -6 -3  4 -4  3  1        (step-2 differences: p(3)-p(1), p(4)-p(2), ... )

  -3 -1 -4  1  2 -2           (step-3 differences: p(4)-p(1), p(5)-p(2), ... )

   2 -2 -7  7 -3              ( etc. )

   1 -5 -1  2

  -2  1 -6

   4 -4

  -1

CROSSREFS

Cf. A008404 (Costas arrays), A213271 (Costas arrays that are derangements), A213338 (Costas arrays that are cyclic), A213339 (Costas arrays that are connected).

Sequence in context: A199889 A293177 A231382 * A307522 A130707 A131562

Adjacent sequences:  A213267 A213268 A213269 * A213271 A213272 A213273

KEYWORD

nonn,hard,more

AUTHOR

Joerg Arndt, Jun 08 2012

STATUS

approved

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Last modified January 27 04:57 EST 2020. Contains 331291 sequences. (Running on oeis4.)