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A215229 Number of length-6 0..k arrays connected end-around, with no sequence of L<n elements immediately followed by itself (periodic "squarefree"). 1
0, 18, 408, 2940, 12600, 40110, 105168, 240408, 496080, 945450, 1690920, 2870868, 4667208, 7313670, 11104800, 16405680, 23662368, 33413058, 46299960, 63081900, 84647640, 112029918, 146420208, 189184200, 241878000, 306265050, 384333768 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Row 6 of A215228.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = n^6 - 6*n^4 + 5*n^3 + 5*n^2 - 5*n.

Conjectures from Colin Barker, Jul 23 2018: (Start)

G.f.: 6*x^2*(3 + 47*x + 77*x^2 - 7*x^3) / (1 - x)^7.

a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) for n>7.

(End)

EXAMPLE

Some solutions for n=5:

..2....1....5....4....3....0....4....5....1....4....2....5....3....1....1....5

..0....3....2....2....1....4....1....4....2....1....3....3....4....4....4....1

..5....4....3....3....2....1....2....2....3....3....1....5....5....1....0....4

..0....5....0....2....4....5....4....0....2....2....3....0....0....5....4....2

..4....1....1....0....0....4....5....4....0....5....4....2....1....2....3....3

..1....2....3....2....5....3....2....3....5....3....5....0....5....0....5....4

CROSSREFS

Cf. A215228.

Sequence in context: A298465 A260655 A318598 * A172135 A005477 A326368

Adjacent sequences:  A215226 A215227 A215228 * A215230 A215231 A215232

KEYWORD

nonn

AUTHOR

R. H. Hardin, Aug 06 2012

STATUS

approved

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Last modified September 28 11:24 EDT 2020. Contains 337393 sequences. (Running on oeis4.)