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A335818
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Decimal expansion of Sum_{k>=1} 1/phi(k)^3, where phi is the Euler totient function.
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5
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2, 4, 7, 6, 1, 9, 4, 7, 4, 8, 1, 6, 5, 0, 2, 5, 7, 9, 4, 3, 2, 6, 8, 5, 5, 4, 4, 4, 1, 2, 5, 1, 4, 5, 1, 6, 0, 0, 4, 5, 4, 5, 6, 8, 5, 6, 3, 5, 5, 2, 8, 4, 3, 8, 4, 3, 4, 5, 7, 0, 7, 8, 7, 9, 1, 5, 0, 9, 4, 9, 0, 3, 0, 1, 1, 7, 5, 1, 2, 4, 5, 8, 1, 7, 6, 2, 8, 0, 1, 3, 4, 6, 1, 5, 2, 6, 7, 3, 8, 9, 3, 3, 2, 8, 9
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OFFSET
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1,1
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COMMENTS
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Sum_{k>=1} 1/phi(k)^m is convergent iff m > 1 (reference Monier). - Bernard Schott, Jan 14 2021
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REFERENCES
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Jean-Marie Monier, Analyse, Exercices corrigés, 2ème année MP, Dunod, 1997, Exercice 3.2.21, pp. 281 and 294.
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LINKS
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FORMULA
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Equals Product_{primes p} (1 + 1/((1 - 1/p)^3 * (p^3 - 1))).
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EXAMPLE
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2.476194748165025794326855444125145160045456856355284384345707879150949...
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MATHEMATICA
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$MaxExtraPrecision = 1000; f[p_] := (1 + 1/((1 - 1/p)^s * (p^s - 1))) /. s -> 3; Do[cc = Rest[CoefficientList[Series[Log[f[1/x]], {x, 0, m}], x]]; Print[f[2] * Exp[N[Sum[Indexed[cc, n]*(PrimeZetaP[n] - 1/2^n), {n, 2, m}], 120]]], {m, 100, 1000, 100}]
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PROG
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(PARI) prodeulerrat(1 + 1/((1 - 1/p)^3 * (p^3 - 1))) \\ Amiram Eldar, Mar 15 2021
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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