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%I #15 Aug 18 2019 04:33:41
%S 9,25,28,36,45,50,52,75,76,81,84,90,98,100,117,121,124,144,148,150,
%T 153,156,175,180,208,225,228,234,242,244,245,252,261,268,275,289,292,
%U 300,304,306,316,324,325,333,338,360,364,369,372,380,388,392,400,405,412
%N Solutions to gcd(sigma(x), phi(x)) < gcd(sigma(core(x)), phi(core(x))), i.e., when A009223(x) < A066086(x) or if A066087(x) < 0.
%H Amiram Eldar, <a href="/A076486/b076486.txt">Table of n, a(n) for n = 1..10000</a>
%e For n=9: sigma(9)=13, phi(9)=6, gcd(13,6)=1, core(9)=3, sigma(3)=4, phi(3)=2, gcd(4,2)=2.
%t ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] cor[x_] := Apply[Times, ba[x]] g1[x_] := GCD[DivisorSigma[1, x], EulerPhi[x]] g2[x_] := GCD[DivisorSigma[1, cor[x]], EulerPhi[cor[x]]] Do[s1=g1[n]; s2=g2[n]; If[Greater[s2, s1], Print[n]], {n, 1, 256}]
%Y Cf. A000010, A000203, A007947, A009223, A023900, A048250, A066086, A066087, A076485.
%K nonn
%O 1,1
%A _Labos Elemer_, Oct 17 2002
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