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 A208722 Number of 2n-bead necklaces labeled with numbers 1..n not allowing reversal, with neighbors differing by exactly 1. 2
 0, 1, 4, 15, 52, 210, 796, 3175, 12468, 49288, 194140, 766110, 3019224, 11905330, 46938192, 185111095, 730148332, 2880799554, 11369141308, 44881708072, 177229210656, 700047776214, 2765947680124, 10931565973950, 43215517211240, 170888480306500 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Andrew Howroyd, Table of n, a(n) for n = 1..100 EXAMPLE All solutions for n=4: ..1....1....3....2....1....2....2....2....2....1....1....1....1....1....1 ..2....2....4....3....2....3....3....3....3....2....2....2....2....2....2 ..1....3....3....2....3....2....4....4....2....3....1....1....3....3....1 ..2....4....4....3....2....3....3....3....3....2....2....2....4....2....2 ..3....3....3....2....1....2....4....2....4....3....1....3....3....3....1 ..2....4....4....3....2....3....3....3....3....4....2....4....2....2....2 ..3....3....3....2....3....4....4....4....4....3....1....3....3....3....3 ..2....2....4....3....2....3....3....3....3....2....2....2....2....2....2 CROSSREFS Diagonal of A208727. Sequence in context: A161125 A027295 A371217 * A057332 A230623 A162978 Adjacent sequences: A208719 A208720 A208721 * A208723 A208724 A208725 KEYWORD nonn AUTHOR R. H. Hardin, Mar 01 2012 EXTENSIONS a(13)-a(26) from Andrew Howroyd, Mar 18 2017 STATUS approved

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Last modified August 14 03:23 EDT 2024. Contains 375146 sequences. (Running on oeis4.)