A328130 Number of n-bead necklace structures with beads of exactly four colors and no adjacent beads having the same color.

0, 0, 0, 1, 1, 5, 10, 33, 83, 237, 640, 1817, 5005, 14099, 39504, 111585, 315235, 894845, 2544220, 7256607, 20738097, 59405343, 170488450, 490221899, 1411923987, 4073098085, 11767069378, 34041318969, 98603778565, 285954140473, 830194632190, 2412764894021, 7018972487319

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=4..7 are:
a(4) = 1: ABCD;
a(5) = 1: ABACD;
a(6) = 5: ABABCD, ABACAD, ABACBD, ABACDC, ABCABD;
a(7) = 10: ABABACD, ABABCAD, ABABCBD, ABABCDC, ABACABD, ABACADC, ABACBCD, ABACBDC, ABACDBC, ABCABCD.

Crossrefs

Column k=4 of A327396.

Cf. A056297, A309673, A327397.

Sequence in context: A304215 A073705 A355900 * A121158 A214650 A032772

Adjacent sequences: A328127 A328128 A328129 * A328131 A328132 A328133

Keyword

nonn

Author

Andrew Howroyd, Oct 04 2019

Extensions

Terms a(24) and beyond from Andrew Howroyd, Oct 09 2019

Status

approved