login
A209119
Number of 7-bead necklaces labeled with numbers -n..n not allowing reversal, with sum zero and avoiding the patterns z z+1 z+2 and z z-1 z-2.
1
25, 865, 7377, 35253, 121117, 336055, 802125, 1712987, 3357255, 6145113, 10639105, 17587647, 27961449, 42994779, 64228807, 93558167, 133282385, 186159325, 255461573, 345038397, 459378989, 603678961, 783912475, 1006905635, 1280412799
OFFSET
1,1
COMMENTS
Row 7 of A209115.
LINKS
FORMULA
Empirical: a(n) = 4*a(n-1) - 7*a(n-2) + 9*a(n-3) - 11*a(n-4) + 12*a(n-5) - 12*a(n-6) + 10*a(n-7) - 6*a(n-8) + 3*a(n-9) - 3*a(n-11) + 6*a(n-12) - 10*a(n-13) + 12*a(n-14) - 12*a(n-15) + 11*a(n-16) - 9*a(n-17) + 7*a(n-18) - 4*a(n-19) + a(n-20) for n > 22.
EXAMPLE
Some solutions for n=6:
-5 -6 -5 -4 -6 -6 -5 -6 -4 -5 -4 -5 -4 -6 -6 -5
-3 -3 -1 -2 -5 2 -2 6 -3 -5 -2 6 -1 2 3 -1
-5 -2 -3 -1 -1 -2 -4 -3 -1 -4 -4 -4 -2 -1 -1 -2
-3 -4 0 -3 4 2 -2 -5 -1 4 6 -4 0 -1 4 6
4 3 -2 6 0 4 2 -2 5 3 1 3 5 6 1 5
6 6 6 0 3 -5 6 6 0 1 2 0 -1 -6 2 0
6 6 5 4 5 5 5 4 4 6 1 4 3 6 -3 -3
CROSSREFS
Sequence in context: A181892 A274469 A223258 * A350983 A224478 A159332
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 05 2012
STATUS
approved