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Search: id:A026023
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| A026023 |
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a(n) = number of (s(0), s(1), ..., s(n)) such that s(i) is a nonnegative integer and |s(i) - s(i-1)| = 1 for i = 1,2,...,n and s(0) = 3. Also a(n) = Sum{T(n,k), k = 0,1,...,[ (n+3)/2 ]}, where T is defined in A026022. |
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1
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| 1, 2, 4, 8, 15, 30, 56, 112, 210, 420, 792, 1584, 3003, 6006, 11440, 22880, 43758, 87516, 167960, 335920, 646646, 1293292, 2496144, 4992288, 9657700, 19315400, 37442160, 74884320, 145422675, 290845350, 565722720, 1131445440, 2203961430, 4407922860
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OFFSET
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0,2
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FORMULA
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a(2n) = C(2n+2, n), a(2n+1) = 2a(2n).
E.g.f.: dif(Bessel_I(1,2x)+2*Bessel_I(2,2x)+Bessel_I(3,2x),x); - Paul Barry (pbarry(AT)wit.ie), Jun 09 2007
O.g.f.:-1/2*(-1+4*x^2+(1-8*x^2+20*x^4-16*x^6)^(1/2))/x^4/(2*x-1) [From Maksym Voznyy (voznyy(AT)mail.ru), Aug 11 2009]
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CROSSREFS
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Sequence in context: A000078 A034338 A166861 this_sequence A077596 A091865 A065494
Adjacent sequences: A026020 A026021 A026022 this_sequence A026024 A026025 A026026
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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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Definition corrected by Herbert Kociemba (kociemba(AT)t-online.de), May 08 2004
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