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A230203
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Numbers k such that sigma(phi(k)) > k.
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4
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5, 7, 9, 11, 13, 17, 19, 21, 23, 25, 26, 27, 29, 31, 33, 35, 37, 38, 39, 41, 43, 45, 47, 49, 51, 52, 53, 55, 56, 57, 59, 61, 62, 63, 65, 67, 69, 71, 73, 74, 75, 76, 77, 79, 81, 82, 83, 85, 86, 87, 88, 89, 91, 93, 95, 97, 99, 101, 103, 104, 105, 107, 109, 111, 112, 113, 115, 116, 117, 119
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OFFSET
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1,1
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COMMENTS
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It seems that the odd number k is not in the sequence if and only if k+2 is a Fermat prime (A019434).
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LINKS
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MAPLE
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for n do if sigma(phi(n))>n then print{n} fi od:
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MATHEMATICA
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Select[Range[150], DivisorSigma[1, EulerPhi[#]]>#&] (* Harvey P. Dale, Apr 14 2019 *)
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PROG
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(PARI) is(k) = sigma(eulerphi(k)) > k; \\ Amiram Eldar, Apr 04 2024
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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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