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 A208666 Number of 2n-bead necklaces labeled with numbers 1..n allowing reversal, with neighbors differing by exactly 1. 1
 0, 1, 4, 14, 44, 152, 514, 1866, 6884, 26137, 100442, 390592, 1526272, 5989223, 23548688, 92727898, 365445200, 1441195226, 5686268314, 22444465311, 88622259788, 350040069245, 1383007946774, 5465854718664, 21607909105528, 85444555330132, 337962745845558, 1337094537703089 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Andrew Howroyd, Table of n, a(n) for n = 1..100 FORMULA a(n) = (2*A208722(n) + A220062(n+1,n))/4. - Andrew Howroyd, Mar 19 2017 EXAMPLE All solutions for n=3: ..1....1....1....2 ..2....2....2....3 ..1....3....1....2 ..2....2....2....3 ..3....3....1....2 ..2....2....2....3 CROSSREFS Diagonal of A208671. Sequence in context: A083377 A047115 A356726 * A125068 A184138 A318019 Adjacent sequences: A208663 A208664 A208665 * A208667 A208668 A208669 KEYWORD nonn AUTHOR R. H. Hardin, Feb 29 2012 EXTENSIONS a(11)-a(28) from Andrew Howroyd, Mar 19 2017 STATUS approved

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Last modified June 4 15:27 EDT 2023. Contains 363128 sequences. (Running on oeis4.)