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A209345 Number of 4-bead necklaces labeled with numbers -n..n allowing reversal, with sum zero with no three beads in a row equal 2
4, 15, 35, 72, 128, 205, 311, 448, 618, 829, 1083, 1382, 1734, 2141, 2605, 3134, 3730, 4395, 5137, 5958, 6860, 7851, 8933, 10108, 11384, 12763, 14247, 15844, 17556, 19385, 21339, 23420, 25630, 27977, 30463, 33090, 35866, 38793, 41873, 45114, 48518, 52087 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 4 of A209344.

LINKS

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

FORMULA

Empirical: a(n) = 3*a(n-1) - 3*a(n-2) + 2*a(n-3) - 3*a(n-4) + 3*a(n-5) - a(n-6).

Empirical g.f.: x*(4 + 3*x + 2*x^2 + 4*x^3 - x^4) / ((1 - x)^4*(1 + x + x^2)). - Colin Barker, Mar 07 2018

EXAMPLE

Some solutions for n=10:

  -5  -5  -9  -5  -7  -2  -9 -10  -9  -4  -7 -10  -4  -6  -7  -7

   1  -3   5   0   1  -1   5   5  -4   1  -1  -3  -4   1   7  -6

  -3  -2  -5   4   4   4  -6  -3   3   0   6  10   3  -2  -7  10

   7  10   9   1   2  -1  10   8  10   3   2   3   5   7   7   3

CROSSREFS

Cf. A209344.

Sequence in context: A113693 A211537 A213420 * A323452 A190093 A077414

Adjacent sequences:  A209342 A209343 A209344 * A209346 A209347 A209348

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 06 2012

STATUS

approved

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Last modified October 15 20:04 EDT 2019. Contains 328037 sequences. (Running on oeis4.)