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A002996
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a(n) = Sum_{k|n} mu(k)*Catalan(n/k) (mu = Moebius function A008683).
(Formerly M3454)
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11
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1, 1, 4, 12, 41, 126, 428, 1416, 4857, 16753, 58785, 207868, 742899, 2674010, 9694799, 35356240, 129644789, 477633711, 1767263189, 6564103612, 24466266587, 91482504853, 343059613649, 1289903937896, 4861946401410, 18367352329251, 69533550911142, 263747949075908, 1002242216651367
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OFFSET
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1,3
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COMMENTS
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REFERENCES
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A. Errera, Analysis situs - Un problème d'énumération, Mémoires Acad. Bruxelles, Classe des sciences, Série 2, Vol. XI, Fasc. 6, No. 1421 (1931), 26 pp.
A. Errera, De quelques problèmes d'analysis situs, Comptes Rend. Congr. Nat. Sci. Bruxelles, (1930), 106-110.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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FORMULA
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G.f.: 1 + Sum_{n>=1} a(n)*x^n/(1 - x^n) = 1/(1 - x/(1 - x/(1 - x/(1 - ...)))). - Ilya Gutkovskiy, May 06 2017
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MATHEMATICA
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Table[Sum[MoebiusMu[k] CatalanNumber[n/k], {k, Divisors[n]}], {n, 30}] (* Harvey P. Dale, Oct 07 2014 *)
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PROG
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(PARI) a(n)=sumdiv(n, d, moebius(n/d)*binomial(2*d, d)/(d+1)); \\ Joerg Arndt, Jun 15 2013
(Haskell)
a002996 n = sum $ zipWith (*) (map a008683 divs) (map a000108 $ reverse divs)
where divs = a027750_row n
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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