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A209348 Number of 7-bead necklaces labelled with numbers -n..n allowing reversal, with sum zero with no three beads in a row equal 1
21, 514, 4029, 18646, 62853, 172610, 409199, 870122, 1699831, 3104474, 5365417, 8858142, 14068115, 21614144, 32266607, 46975088, 66888951, 93389664, 128113109, 172986976, 230254897, 302518564, 392763779, 504407780, 641326401, 807907094 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 7 of A209344

LINKS

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

FORMULA

Empirical: a(n) = 3*a(n-1) -2*a(n-2) -a(n-3) +a(n-4) -2*a(n-5) +5*a(n-6) -5*a(n-7) +3*a(n-8) -3*a(n-10) +5*a(n-11) -5*a(n-12) +2*a(n-13) -a(n-14) +a(n-15) +2*a(n-16) -3*a(n-17) +a(n-18)

EXAMPLE

Some solutions for n=5

.-5...-4...-4...-5...-5...-4...-4...-3...-2...-2...-4...-4...-5...-5...-5...-4

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

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

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

.-4...-3....2....1...-1....2....5....2...-1....3....5...-4....3....2...-2....1

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

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

CROSSREFS

Sequence in context: A231542 A065921 A129993 * A095655 A221766 A080483

Adjacent sequences:  A209345 A209346 A209347 * A209349 A209350 A209351

KEYWORD

nonn

AUTHOR

R. H. Hardin Mar 06 2012

STATUS

approved

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Last modified November 26 10:00 EST 2014. Contains 250038 sequences.