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A190503 Numbers n such that sigma(phi(n)) divides sigma(n). 3
1, 2, 6, 12, 14, 22, 24, 28, 44, 46, 48, 56, 68, 87, 88, 92, 94, 96, 112, 118, 166, 174, 176, 184, 188, 192, 214, 224, 236, 332, 334, 352, 358, 362, 368, 376, 384, 390, 410, 428, 448, 454, 472, 526, 664, 668, 694, 704, 716, 718, 736, 752, 766, 768, 856, 896 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

These numbers appear indirectly in A067740, which seeks the least k such that sigma(k)/sigma(phi(k)) = n. Most of these numbers are even. The odd terms (1, 87, 1257, 41559, 56679,...) all appear to produce sigma(n)/sigma(phi(n)) = 1.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

MATHEMATICA

Select[Range[1000], IntegerQ[DivisorSigma[1, #]/DivisorSigma[1, EulerPhi[#]]] &]

CROSSREFS

Cf. A033631 (n such that sigma(n)/sigma(phi(n)) = 1), A067740.

Cf. A066831 (n such that sigma(n) divides sigma(phi(n))).

Sequence in context: A333833 A057895 A111369 * A320149 A140760 A161922

Adjacent sequences:  A190500 A190501 A190502 * A190504 A190505 A190506

KEYWORD

nonn

AUTHOR

T. D. Noe, May 11 2011

STATUS

approved

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Last modified June 6 18:59 EDT 2020. Contains 334832 sequences. (Running on oeis4.)