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A293708
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Numbers n such that phi(sigma(n))/n > phi(sigma(m))/m for all m < n, where sigma is the sum of divisors function (A000203) and phi is Euler's totient function (A000010).
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0
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1, 4, 16, 36, 144, 576, 3600, 14400, 32400, 129600, 291600, 1166400, 8643600, 34574400, 77792400, 84272400, 311169600, 337089600, 700131600, 2800526400, 179233689600, 202338032400, 809352129600
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OFFSET
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1,2
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COMMENTS
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Makowski and Schinzel proved that lim sup phi(sigma(n))/n = oo, thus this sequence is infinite.
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LINKS
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MATHEMATICA
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a={}; rm=0; Do[r = EulerPhi[DivisorSigma[1, n]]/n; If[r>rm, rm=r; AppendTo[a, n]], {n, 1, 100000}]; a
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PROG
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(PARI) lista(nn) = {my(rmax = 0); for (n=1, nn, if ((r=eulerphi(sigma(n))/n) > rmax, rmax = r; print1(n, ", ")); ); } \\ Michel Marcus, Oct 18 2017
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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