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A209488
Number of 7-bead necklaces labeled with numbers -n..n allowing reversal, with sum zero and avoiding the patterns z z+1 z+2 and z z-1 z-2.
1
15, 458, 3740, 17771, 60778, 168453, 401634, 857433, 1679810, 3074315, 5321674, 8796771, 13984178, 21501971, 32119660, 46785813, 66648788, 93089119, 127741326, 172532039, 229703658, 301856427, 391974770, 503474661, 640230118, 806627193
OFFSET
1,1
COMMENTS
Row 7 of A209485.
LINKS
FORMULA
Empirical: a(n) = 2*a(n-1) - a(n-3) - a(n-5) + a(n-6) - 2*a(n-7) + 2*a(n-8) + a(n-9) - a(n-13) - 2*a(n-14) + 2*a(n-15) - a(n-16) + a(n-17) + a(n-19) - 2*a(n-21) + a(n-22) for n > 24.
EXAMPLE
Some solutions for n=5:
-3 -4 -4 -4 -4 -4 -2 -5 -4 -4 -5 -4 -4 -5 -4 -5
-1 -1 -4 -3 0 -3 -1 -4 -4 -2 5 2 -2 -4 1 -1
-2 0 2 4 -1 -1 -2 5 -4 2 -4 3 0 5 1 3
4 -2 2 -3 4 -1 0 3 2 1 -2 -3 1 0 -3 -5
-3 3 3 4 0 4 3 -5 5 -3 -2 -1 4 1 1 4
0 4 -3 1 1 5 -2 1 1 3 3 -1 -1 -1 1 5
5 0 4 1 0 0 4 5 4 3 5 4 2 4 3 -1
CROSSREFS
Sequence in context: A369828 A306675 A219561 * A361307 A320097 A177080
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 09 2012
STATUS
approved