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A067709
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Numbers k such that phi(2*sigma(k)) = 2*sigma(phi(k)).
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1
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2, 4, 16, 18, 64, 100, 450, 516, 1458, 4096, 4624, 13932, 14406, 20124, 21780, 28900, 29262, 29616, 36450, 45996, 62500, 65536, 92778, 95916, 106092, 106308, 114630, 114930, 121872, 125652, 130050, 140130, 145794, 149124, 160986, 179562, 185100
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OFFSET
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1,1
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COMMENTS
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LINKS
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MAPLE
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MATHEMATICA
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Select[Range[200000], EulerPhi[2*DivisorSigma[1, #]] == 2*DivisorSigma[1, EulerPhi[#]] &] (* Amiram Eldar, May 13 2022 *)
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PROG
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(PARI) isok(k) = eulerphi(2*sigma(k)) == 2*sigma(eulerphi(k)); \\ Michel Marcus, May 13 2022
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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