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A255618
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Number of length n+4 0..2 arrays with at most two downsteps in every 4 consecutive neighbor pairs.
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1
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237, 694, 2040, 5997, 17622, 51768, 152106, 446932, 1313199, 3858468, 11337057, 33310953, 97875387, 287580727, 844979241, 2482746381, 7294888809, 21434086890, 62978352609, 185045107303, 543705739710, 1597534436091, 4693929248088
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 3*a(n-1) -a(n-3) +3*a(n-4) -3*a(n-5) -8*a(n-6) +9*a(n-7) -3*a(n-8) +a(n-9).
Empirical g.f.: x*(237 - 17*x - 42*x^2 + 114*x^3 - 386*x^4 - 429*x^5 + 657*x^6 - 216*x^7 + 81*x^8) / ((1 - x)*(1 - 2*x - 2*x^2 - x^3 - 4*x^4 - x^5 + 7*x^6 - 2*x^7 + x^8)). - Colin Barker, Jan 24 2018
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EXAMPLE
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Some solutions for n=4:
1 0 2 0 1 2 2 1 2 2 2 2 0 2 1 0
0 0 1 1 2 1 1 1 2 0 0 0 2 2 0 0
0 2 2 2 0 2 1 1 1 2 0 2 0 1 2 1
1 1 1 2 2 0 2 2 0 2 1 2 0 2 0 2
2 1 1 0 2 0 2 2 2 2 2 1 2 1 2 0
2 2 1 0 1 0 0 1 2 0 2 1 2 1 0 2
1 0 1 2 2 2 0 0 1 1 0 1 1 2 0 0
2 1 0 0 0 1 0 0 2 2 2 0 2 2 1 0
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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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