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A208717
Number of n-bead necklaces labeled with numbers 1..4 allowing reversal, with no adjacent beads differing by more than 1.
1
4, 7, 10, 18, 28, 56, 98, 208, 418, 933, 2044, 4777, 11072, 26548, 63672, 155248, 379348, 935278, 2311294, 5741228, 14292966, 35699049, 89339860, 224097602, 563074848, 1417313897, 3572747650, 9019154944, 22797181996, 57693378135, 146168107034, 370712004868
OFFSET
1,1
LINKS
FORMULA
a(2n+1) = (1/2) * (A208773(2n+1) + A126358(n+1)). - Andrew Howroyd, Mar 03 2017
a(2n) = (1/2) * A208773(2n) + (1/4) * (A126358(n) + A126358(n+1)). - Andrew Howroyd, Mar 03 2017
EXAMPLE
All solutions for n=3:
..3....2....1....3....4....2....3....1....1....2
..3....2....1....3....4....3....4....1....2....2
..4....2....1....3....4....3....4....2....2....3
CROSSREFS
Column 4 of A208721.
Sequence in context: A310718 A310719 A103408 * A208773 A088408 A027752
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 01 2012
EXTENSIONS
a(29)-a(32) from Andrew Howroyd, Mar 03 2017
STATUS
approved