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A327397 Number of n-bead necklace structures with beads of exactly three colors and no adjacent beads having the same color. 4
0, 0, 1, 1, 1, 3, 3, 7, 11, 19, 31, 63, 105, 201, 367, 695, 1285, 2451, 4599, 8775, 16651, 31837, 60787, 116639, 223697, 430395, 828525, 1598227, 3085465, 5965999, 11545611, 22370999, 43383571, 84217615, 163617805, 318150719, 619094385, 1205614053, 2349384031 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

Colors may be permuted without changing the necklace structure.

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..200

EXAMPLE

Necklace structures for n=3..8 are:

  a(3) = 1: ABC;

  a(4) = 1: ABAC;

  a(5) = 1: ABABC;

  a(6) = 3: ABABAC, ABACBC, ABCABC;

  a(7) = 3: ABABABC, ABABCAC, ABACABC;

  a(8) = 7: ABABABAC, ABABACAC, ABABACBC, ABABCABC, ABABCBAC, ABACABAC, ABACBABC.

CROSSREFS

Column k=3 of A327396.

Cf. A056296, A306888, A328130.

Sequence in context: A292141 A022403 A082550 * A036056 A278789 A279829

Adjacent sequences:  A327394 A327395 A327396 * A327398 A327399 A327400

KEYWORD

nonn

AUTHOR

Andrew Howroyd, Oct 04 2019

EXTENSIONS

Terms a(33) and beyond from Andrew Howroyd, Oct 09 2019

STATUS

approved

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Last modified November 17 06:06 EST 2019. Contains 329217 sequences. (Running on oeis4.)