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A220613
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Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly two horizontal and vertical neighbors, without consecutive collinear links
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1
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1, 21, 85, 781, 4673, 34981, 233265, 1653229, 11354857, 79290645, 548972737, 3817993565, 26491584361, 184040357765, 1277739038129, 8873937621293, 61619077914745, 427911161639829, 2971470559369153, 20634790487757629
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 5*a(n-1) +40*a(n-2) -144*a(n-3) -532*a(n-4) +1484*a(n-5) +3044*a(n-6) -6644*a(n-7) -8872*a(n-8) +13920*a(n-9) +13824*a(n-10) -13056*a(n-11) -10688*a(n-12) +4288*a(n-13) +3072*a(n-14)
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EXAMPLE
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Some solutions for n=3 0=self 2=n 4=w 6=e 8=s (reciprocal directions total 10)
.68.48.00.68.48.00.00...68.48.68.48.00.00.00...00.00.00.68.48.00.00
.26.24.00.26.24.00.00...26.24.26.24.00.68.48...00.00.00.26.24.68.48
.00.00.00.00.00.00.00...00.00.00.00.00.26.24...00.00.00.00.00.26.24
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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