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 A208723 Number of 2n-bead necklaces labeled with numbers 1..4 not allowing reversal, with neighbors differing by exactly 1. 2
 3, 5, 8, 15, 27, 60, 123, 285, 648, 1529, 3603, 8680, 20883, 50825, 124056, 304575, 750123, 1855100, 4600203, 11442087, 28527448, 71292605, 178526883, 447919420, 1125750147, 2833906685, 7144450568, 18036423975, 45591631803, 115381823348 (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) = (1/n) * Sum_{d | n} totient(n/d) * A005248(d). - Andrew Howroyd, Mar 18 2017 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 Column 4 of A208727. Sequence in context: A052977 A191633 A215327 * A285010 A352917 A099846 Adjacent sequences: A208720 A208721 A208722 * A208724 A208725 A208726 KEYWORD nonn AUTHOR R. H. Hardin, Mar 01 2012 EXTENSIONS a(26)-a(30) from Andrew Howroyd, Mar 18 2017 STATUS approved

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Last modified August 7 03:39 EDT 2024. Contains 375008 sequences. (Running on oeis4.)