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A340461
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a(n) = 2*sigma(phi(n)) - n.
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0
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1, 0, 3, 2, 9, 0, 17, 6, 15, 4, 25, 2, 43, 10, 15, 14, 45, 6, 59, 10, 35, 14, 49, 6, 59, 30, 51, 28, 83, 0, 113, 30, 51, 28, 85, 20, 145, 40, 81, 22, 139, 14, 149, 40, 75, 26, 97, 14, 143, 34, 75, 68, 143, 24, 125, 64, 125, 54, 121, 2, 275, 82, 119, 62, 183, 18, 221, 58, 99
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OFFSET
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1,3
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COMMENTS
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In 1964, A. Mąkowski and A. Schinzel conjectured that sigma(phi(n))/n >= 1/2 for all n (see links Mąkowski & Schinzel and Graeme L. Cohen), equivalent to a(n) >= 0.
In 1992, K. Atanassov believed that he obtained a proof of this conjecture but his proof was valid only for certain special values of n (see link József Sándor).
Mrs. K. Kuhn checked that this inequality holds for all positive integers n having at most six prime factors (see A. Grytczuk, et al.).
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REFERENCES
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Richard K. Guy, Unsolved Problems in Number Theory, 3rd Edition, Springer, 2004, Section B42, pp. 150-152.
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LINKS
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FORMULA
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EXAMPLE
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phi(5) = 4, sigma(4) = 7 and a(5) = 2 * sigma(phi(5)) - 5 = 2*7-5 = 9.
phi(30) = 8, sigma(8) = 15 and a(30) = 2 * sigma(phi(30)) - 30 = 0.
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MAPLE
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with(numtheory):
E := seq(2*sigma(phi(n))-n, n=1..100);
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MATHEMATICA
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a[n_] := 2 * DivisorSigma[1, EulerPhi[n]] - n; Array[a, 100] (* Amiram Eldar, Jan 08 2021 *)
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PROG
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(PARI) a(n) = 2*sigma(eulerphi(n)) - n; \\ Michel Marcus, Jan 08 2021
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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