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Search: id:A163970
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| A163970 |
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G.f.: A(x) = tanh( Sum_{n>=1} 2^((2n-1)^2)*x^(2n-1)/(2n-1) ). |
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2
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| 2, 168, 6710208, 80421395017344, 268650181814894062310400, 241677817414364648836194235222953984, 57560679870262286682598360350282651217048664506368
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OFFSET
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1,1
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COMMENT
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Note that x = tanh( Sum_{n>=1} x^(2n-1)/(2n-1) ).
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FORMULA
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G.f.: A(x) = [G(x) - G(-x)]/[G(x) + G(-x)], where G(x) = g.f. of A155200.
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EXAMPLE
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G.f.: A(x) = 2*x + 168*x^3 + 6710208*x^5 + 80421395017344*x^7 +...
atanh(A(x)) = 2*x + 2^9*x^3/3 + 2^25*x^5/5 + 2^49*x^7/7 +...
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PROGRAM
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(PARI) {a(n)=polcoeff(tanh(sum(k=1, 2*n, 2^((2*k-1)^2)*x^(2*k-1)/(2*k-1)+x*O(x^(2*n)))), 2*n-1)}
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CROSSREFS
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Cf. A155200, A163971.
Sequence in context: A142602 A005020 A157316 this_sequence A007760 A051030 A139935
Adjacent sequences: A163967 A163968 A163969 this_sequence A163971 A163972 A163973
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KEYWORD
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nonn
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AUTHOR
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Paul D. Hanna (pauldhanna(AT)juno.com), Aug 14 2009
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