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A026017
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a(n) = number of (s(0), s(1), ..., s(2n-1)) such that s(i) is a nonnegative integer and |s(i) - s(i-1)| = 1 for i = 1,2,...,n, s(0) = 2, s(2n-1) = 5. Also a(n) = T(2n-1,n-2), where T is the array defined in A026009.
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2
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1, 5, 21, 83, 319, 1209, 4550, 17068, 63954, 239666, 898909, 3375825, 12697035, 47833905, 180510210, 682341000, 2583591150, 9798281910, 37218303330, 141585223494, 539395269462, 2057771255210, 7860697923436, 30065829471048, 115135255095140, 441410428339972
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OFFSET
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2,2
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LINKS
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FORMULA
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Expansion of (1+x^1*C^3)*C^4, where C = (1-(1-4*x)^(1/2))/(2*x) is g.f. for Catalan numbers, A000108.
Conjecture: (n+4)*a(n) +(-8*n-17)*a(n-1) +(19*n+1)*a(n-2) +6*(-2*n+5)*a(n-3)=0. - R. J. Mathar, Jun 20 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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