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A230371 Numbers n such that sigma(phi(n)) = sigma(n) - phi(n). 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Tested up to n = 10^6.

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..228 (terms < 3*10^10)

EXAMPLE

phi(172) = 84, sigma(172) = 308, sigma(84) = 224 and 308 - 84 = 224.

MAPLE

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);

MATHEMATICA

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 *)

CROSSREFS

Cf. A000010, A000203, A062402, A230023, A230372.

Sequence in context: A224555 A146339 A067356 * A056132 A261706 A043387

Adjacent sequences:  A230368 A230369 A230370 * A230372 A230373 A230374

KEYWORD

nonn

AUTHOR

Paolo P. Lava, Oct 17 2013

STATUS

approved

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Last modified July 22 17:02 EDT 2019. Contains 325225 sequences. (Running on oeis4.)