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A230371
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Numbers n such that sigma(phi(n)) = sigma(n) - phi(n).
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2
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172, 248, 765, 4712, 8924, 16898, 28552, 50692, 99302, 229845, 279490, 280456, 292995, 300430, 323488, 334990, 338990, 346318, 376790, 403790, 521738, 548504, 617918, 1445824, 1625806, 2642596, 2967724, 3935764, 7878836, 8751946, 8810865, 9346790, 11741128
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OFFSET
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1,1
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COMMENTS
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Tested up to n = 10^6.
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LINKS
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EXAMPLE
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phi(172) = 84, sigma(172) = 308, sigma(84) = 224 and 308 - 84 = 224.
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MAPLE
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with(numtheory); P:=proc(q) local n;
for n from 1 to q do
if sigma(phi(n))=sigma(n)-phi(n) then print(n);
fi; od; end: P(10^6);
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MATHEMATICA
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dpQ[n_]:=Module[{p=EulerPhi[n]}, DivisorSigma[1, p]==DivisorSigma[1, n]-p]; Select[Range[12*10^6], dpQ] (* Harvey P. Dale, Apr 27 2016 *)
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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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