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%I #11 Mar 30 2023 16:49:54
%S 1,1,3,1,5,3,7,1,9,10,11,3,13,7,1,1,17,9,19,5,1,22,23,1,25,13,3,7,29,
%T 2,31,4,33,17,35,9,37,19,13,20,41,1,43,11,15,46,47,3,49,25,17,52,53,3,
%U 11,7,19,29,59,1,61,31,3,1,65,66,67,17,23,70
%N a(n) is the denominator of sigma(sigma(n))/n.
%H Robert Israel, <a href="/A318060/b318060.txt">Table of n, a(n) for n = 1..10000</a>
%e For n=2, sigma(sigma(n)) = 4, so a(2) = 1.
%p seq(denom((numtheory:-sigma@@2)(n)/n),n=1..200); # _Robert Israel_, Aug 15 2018
%t Table[(DivisorSigma[1,DivisorSigma[1,n]])/n,{n,70}]//Denominator (* _Harvey P. Dale_, Mar 30 2023 *)
%o (PARI) a(n) = denominator(sigma(sigma(n))/n);
%Y Cf. A000203 (sigma), A051027.
%Y Cf. A019278 (where a(n) = 1), A318059 (numerator).
%K nonn,frac
%O 1,3
%A _Michel Marcus_, Aug 14 2018
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