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Search: id:A006025
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| A006025 |
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Number of labeled mating digraphs with n nodes.
(Formerly M3160)
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+0
5
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| 1, 3, 54, 3750, 1009680, 1058347920, 4375678520640, 71934792452208000, 4719774805970453006400, 1237727595442264073683462080, 1298006134163762816201615178698880, 5444432200219729912412940250057668378240
(list; graph; listen)
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OFFSET
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1,2
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
R. C. Read, The Enumeration of Mating-Type Graphs. Report CORR 89-38, Dept. Combinatorics and Optimization, Univ. Waterloo, 1989.
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FORMULA
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a(n) = Sum_{k=0..n} stirling1(n, k)*2^(k^2-k). - Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 11 2003
E.g.f.: -1 + Sum_{n>=0} 2^(n(n-1))*log(1+x)^n/n!. [From Paul D. Hanna (pauldhanna(AT)juno.com), May 20 2009]
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PROGRAM
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(PARI) a(n)=n!*polcoeff(sum(k=0, n, 2^(k*(k-1))*log(1+x+x*O(x^n))^k/k!), n) [From Paul D. Hanna (pauldhanna(AT)juno.com), May 20 2009]
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CROSSREFS
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Cf. A006024.
Sequence in context: A157550 A091826 A091796 this_sequence A049414 A003027 A054545
Adjacent sequences: A006022 A006023 A006024 this_sequence A006026 A006027 A006028
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KEYWORD
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nonn
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AUTHOR
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Simon Plouffe (simon.plouffe(AT)gmail.com)
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EXTENSIONS
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More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 11 2003
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