%I #19 Sep 08 2022 08:46:06
%S 1,35,119,527,775,819,923,2159,2759,3335,5543,6815,6887,12319,13175,
%T 13919,21449,23939,24779,37883,47959,64235,83435,111887,124775,127535,
%U 128375,128615,167195,189143,206735,221135,240239,254939,278963,343655,351995,357599,373319
%N Nonprime terms in A210494.
%H Amiram Eldar, <a href="/A230214/b230214.txt">Table of n, a(n) for n = 1..270</a> (terms 1..95 from Vincenzo Librandi)
%H Umberto Cerruti, <a href="http://www.personalweb.unito.it/umberto.cerruti/pdfblog/numeri-armonici.pdf">Numeri Armonici e Numeri Perfetti</a>, <a href="http://www.personalweb.unito.it/umberto.cerruti/mathblog.html">Blog matematico</a> (in Italian), 2013. The sequence is on page 13.
%t B[n_] := (n DivisorSigma[0, n] + DivisorSigma[2, n])/(2 DivisorSigma[1, n]); Select[Range[5 10^5], IntegerQ[B[#]] && ! PrimeQ[#] &]
%o (Magma) IsInteger := func<i | i eq Floor(i)>; [n: n in [1..5*10^5] | IsInteger((n*NumberOfDivisors(n)+DivisorSigma(2,n))/(2*SumOfDivisors(n))) and not IsPrime(n)];
%Y Cf. A210494.
%K nonn
%O 1,2
%A _Bruno Berselli_, Oct 11 2013