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A230201
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Numbers k such that sigma(phi(k)) < k.
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4
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2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 30, 32, 34, 36, 40, 42, 44, 46, 48, 50, 54, 58, 60, 64, 66, 68, 70, 72, 78, 80, 84, 90, 92, 94, 96, 98, 100, 102, 106, 108, 110, 114, 118, 120, 126, 128, 130, 132, 136, 138, 140, 144, 150, 156, 160, 162, 166, 168
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OFFSET
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1,1
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COMMENTS
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All terms are even. However, sigma(phi(k)) may be equal to k for an odd number k if k+2 is a Fermat prime.
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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[200], DivisorSigma[1, EulerPhi[#]] < # &] (* T. D. Noe, Oct 14 2013 *)
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PROG
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(PARI) isok(n) = sigma(eulerphi(n)) < n; \\ Michel Marcus, Oct 12 2013
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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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