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%I #14 Feb 09 2017 06:12:15
%S 1,2,3,4,7,9,16,18,21,22,25,31,32,49,50,52,64,66,70,81,93,94,97,98,
%T 100,115,119,121,127,144,156,162,169,170,196,210,214,217,225,241,242,
%U 256,265,282,289,291,310,322,337,338,343,345,357,361,364,381,382,385,400
%N Numbers n such that gcd(sigma(n), sigma(sigma(n)))=1.
%C In other words, numbers n such that A000203(n) is in A014567. - _Ivan Neretin_, Feb 08 2017
%H Ivan Neretin, <a href="/A067236/b067236.txt">Table of n, a(n) for n = 1..10000</a>
%t ds1Q[n_]:=Module[{ds=DivisorSigma[1,n]},GCD[ds,DivisorSigma[1,ds]]==1]; Select[Range[500],ds1Q] (* _Harvey P. Dale_, Jun 13 2014 *)
%o (PARI) isok(n) = gcd(sigma(n), sigma(sigma(n))) == 1; \\ _Michel Marcus_, Feb 08 2017
%Y Cf. A000203, A051027.
%K nonn
%O 1,2
%A _Benoit Cloitre_, Feb 20 2002
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