This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A230214 #19 Sep 08 2022 08:46:06 %S A230214 1,35,119,527,775,819,923,2159,2759,3335,5543,6815,6887,12319,13175, %T A230214 13919,21449,23939,24779,37883,47959,64235,83435,111887,124775,127535, %U A230214 128375,128615,167195,189143,206735,221135,240239,254939,278963,343655,351995,357599,373319 %N A230214 Nonprime terms in A210494. %H A230214 Amiram Eldar, <a href="/A230214/b230214.txt">Table of n, a(n) for n = 1..270</a> (terms 1..95 from Vincenzo Librandi) %H A230214 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 A230214 B[n_] := (n DivisorSigma[0, n] + DivisorSigma[2, n])/(2 DivisorSigma[1, n]); Select[Range[5 10^5], IntegerQ[B[#]] && ! PrimeQ[#] &] %o A230214 (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 A230214 Cf. A210494. %K A230214 nonn %O A230214 1,2 %A A230214 _Bruno Berselli_, Oct 11 2013