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A026087
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a(n) = number of (s(0), s(1), ..., s(n)) such that every s(i) is an integer, s(0) = 0, |s(i) - s(i-1)| = 1 for i = 1,2,3; |s(i) - s(i-1)| <= 1 for i >= 4, s(n) = 4. Also a(n) = T(n,n-4), where T is the array defined in A026082.
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0
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1, 2, 9, 28, 93, 294, 925, 2872, 8856, 27136, 82764, 251472, 761774, 2301924, 6941898, 20899680, 62834397, 188690634, 566081421, 1696873148, 5082959517, 15216909686, 45532045749, 136182428520, 407160436435, 1216953379486, 3636353333187
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OFFSET
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4,2
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LINKS
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FORMULA
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Conjecture: -(n-4)*(n+4)*a(n) +(4*n^2-11*n-27)*a(n-1) +(-2*n^2+29*n-24)*a(n-2) -(4*n+5)*(n-5)*a(n-3) +3*(n-5)*(n-6)*a(n-4)=0. - R. J. Mathar, Jun 23 2013
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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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