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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 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 August 6 11:55 EDT 2020. Contains 336246 sequences. (Running on oeis4.)