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%I #13 May 17 2024 03:26:24
%S 1,2,6,12,14,22,24,28,44,46,48,56,68,87,88,92,94,96,112,118,166,174,
%T 176,184,188,192,214,224,236,332,334,352,358,362,368,376,384,390,410,
%U 428,448,454,472,526,664,668,694,704,716,718,736,752,766,768,856,896
%N Numbers k such that sigma(phi(k)) divides sigma(k).
%C 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(k)/sigma(phi(k)) = 1.
%H T. D. Noe, <a href="/A190503/b190503.txt">Table of n, a(n) for n = 1..1000</a>
%t Select[Range[1000], IntegerQ[DivisorSigma[1,#]/DivisorSigma[1,EulerPhi[#]]] &]
%o (PARI) is(k) = {my(f = factor(k), s = sigma(f), p = eulerphi(f)); !(s % sigma(p));} \\ _Amiram Eldar_, May 17 2024
%Y Cf. A000010 (phi), A000203 (sigma), A062402, A067740.
%Y Cf. A033631 (k such that sigma(k)/sigma(phi(k)) = 1).
%Y Cf. A066831 (k such that sigma(k) divides sigma(phi(k))).
%K nonn
%O 1,2
%A _T. D. Noe_, May 11 2011
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