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 A208670 Number of 2n-bead necklaces labeled with numbers 1..7 allowing reversal, with neighbors differing by exactly 1. 1
 6, 11, 20, 41, 86, 208, 514, 1398, 3934, 11576, 34850, 107303, 334396, 1053851, 3345320, 10685570, 34292064, 110498897, 357256018, 1158492478, 3766458404, 12274037845, 40082339406, 131144365904, 429838330172, 1411104048106, 4639351259122, 15273992343065 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Andrew Howroyd, Table of n, a(n) for n = 1..100 FORMULA a(n) = (2*A208726(n) + A129639(11+n))/4. EXAMPLE All solutions for n=3: ..1....5....1....5....3....4....1....6....4....1....2....2....4....5....3....4 ..2....6....2....6....4....5....2....7....5....2....3....3....5....6....4....5 ..1....5....3....7....3....4....1....6....6....3....4....2....6....5....5....4 ..2....6....2....6....4....5....2....7....5....4....3....3....7....6....4....5 ..3....5....3....7....5....6....1....6....6....3....4....2....6....7....5....4 ..2....6....2....6....4....5....2....7....5....2....3....3....5....6....4....5 .. ..2....2....3....3 ..3....3....4....4 ..2....4....3....5 ..3....5....4....6 ..4....4....3....5 ..3....3....4....4 CROSSREFS Column 7 of A208671. Sequence in context: A188556 A021011 A000382 * A208726 A192750 A000383 Adjacent sequences:  A208667 A208668 A208669 * A208671 A208672 A208673 KEYWORD nonn AUTHOR R. H. Hardin, Feb 29 2012 EXTENSIONS a(12)-a(28) from Andrew Howroyd, Mar 19 2017 STATUS approved

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