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 A168129 #19 Feb 22 2020 08:31:10 %S A168129 1,4,30,444,1767,86250,97920,185700,584640,21954842,17654544432, %T A168129 357550809280,709346653572,1061551370880 %N A168129 Numbers sigma(k) when Sum_(j=1..k) sigma(j) / sigma(k) is an integer. %C A168129 Numbers A000203(k) when A024916(k) / A000203(k) is an integer. %C A168129 Corresponding values of k, Sum_(j=1..k) sigma(k) and Sum_(j=1..k) sigma(j)/sigma(k) are given in A168127, A168130 and A168128. - _Jaroslav Krizek_, Nov 21 2009 %F A168129 a(n) = A000203(A168127(n)). - _Michel Marcus_, Feb 22 2020 %e A168129 a(3) = 30 because A024916(29) / A000203(29) = 690 / 30 = 23 is an integer, where 29 is A168127(3). %o A168129 (PARI) v=vector(10); c=0; m=0; for(k=1, 11413204, s=sigma(k); m=m+s; if(m%s==0, c++; v[c]=s)); v=vecsort(v); for(i=1, c, print1(v[i] ", ")) \\ _Donovan Johnson_, Oct 16 2013 %Y A168129 Cf. A000203, A024916, A168127, A168128, A168130. %K A168129 nonn,more %O A168129 1,2 %A A168129 _Jaroslav Krizek_, Nov 18 2009, Dec 04 2009 %E A168129 a(8)-a(10) from _Donovan Johnson_, Oct 16 2013 %E A168129 a(11)-a(14) from _Giovanni Resta_, Jun 06 2016 %E A168129 Name edited by _Michel Marcus_, Feb 22 2020