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Search: id:A138903
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| A138903 |
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a(n) = (1/2^n)* Sum_{k=0..n} binomial(n,k)*(n+k)^(n-1). |
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+0
2
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| 1, 3, 21, 234, 3590, 70254, 1672972, 46955760, 1517994792, 55549351800, 2269918543640, 102452561694864, 5062050729973120, 271751784988056576, 15750949414628405760, 980315266648197537792, 65207656047198387921536
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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E.g.f.: A(x) = ln(B(x)), where B(x) is e.g.f. of A138860.
E.g.f: A(x) = Series_Reversion[ 2*x/(exp(x) + exp(2*x)) ].
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MAPLE
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A138903 := proc(n) local k ; add(binomial(n, k)*(n+k)^(n-1), k=0..n)/2^n ; end: seq(A138903(n), n=1..20) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 12 2008
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PROGRAM
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(PARI) {a(n)=local(X=x+x*O(x^n)); n!*polcoeff(serreverse(2*x/(exp(X)+exp(2*X)) ), n)}
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CROSSREFS
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Sequence in context: A008545 A005373 A078586 this_sequence A058562 A145083 A138213
Adjacent sequences: A138900 A138901 A138902 this_sequence A138904 A138905 A138906
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Hanna and Vladeta Jovovic (vladeta(AT)eunet.rs), Apr 02 2008, Apr 03 2008
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 12 2008
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