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%I #17 Apr 04 2024 07:55:39
%S 1,2,7,2,12,14,15,3,14,39,28,14,24,30,4,2,39,28,42,24,3,91,60,7,32,48,
%T 10,30,72,13,63,13,124,60,124,28,60,84,40,117,96,6,84,56,56,195,124,
%U 14,80,64,65,171,120,20,39,45,62,117,168,8,96,126,10,2,224,403,126,78,84,403
%N a(n) is the numerator of sigma(sigma(n))/n.
%H Robert Israel, <a href="/A318059/b318059.txt">Table of n, a(n) for n = 1..10000</a>
%F For n=2, sigma(sigma(n)) = 4, so a(2) = 2.
%e Fractions begin with 1, 2, 7/3, 2, 12/5, 14/3, 15/7, 3, 14/9, 39/10, 28/11, 14/3, ...
%p seq(numer((numtheory:-sigma@@2)(n)/n),n=1..100); # _Robert Israel_, Aug 14 2018
%t a[n_] := Numerator[DivisorSigma[1, DivisorSigma[1, n]]/n]; Array[a, 100] (* _Amiram Eldar_, Apr 04 2024 *)
%o (PARI) a(n) = numerator(sigma(sigma(n))/n);
%Y Cf. A000203 (sigma), A051027.
%Y Cf. A098223 (when denominator is 1), A318060 (denominator).
%K nonn,frac
%O 1,2
%A _Michel Marcus_, Aug 14 2018
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