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Search: id:A026013
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| A026013 |
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a(n) = number of (s(0), s(1), ..., s(2n)) 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) = 4. Also a(n) = T(2n,n-1), where T is the array defined in A026009. |
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+0
2
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| 1, 4, 15, 55, 200, 726, 2639, 9620, 35190, 129200, 476102, 1760673, 6533150, 24319050, 90795375, 339929880, 1275977670, 4801199400, 18106714050, 68430306750, 259129680264, 983085703116, 3736124441990, 14222020085880, 54221213973500
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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G.f.: (x + x^2*C^3)*C^3 where C = g.f. for Catalan numbers A000108.
E.g.f.: exp(2x)(Bessel_I(1,2x)-Bessel_I(4,2x)); - Paul Barry (pbarry(AT)wit.ie), Jun 04 2007
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CROSSREFS
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Adjacent sequences: A026010 A026011 A026012 this_sequence A026014 A026015 A026016
Sequence in context: A126932 A094833 A039717 this_sequence A050183 A094375 A047018
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KEYWORD
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nonn
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AUTHOR
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Clark Kimberling (ck6(AT)evansville.edu)
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EXTENSIONS
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Corrected by Franklin T. Adams-Watters, Oct 25 2006
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