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 A284755 #7 Feb 16 2025 08:33:43
%S A284755 2,3,63,1249,4696,1200509
%N A284755 Numbers n such that the average of all proper divisors of all positive integers <= n is an integer.
%C A284755 Numbers n such that A002541(n)|A153485(n).
%C A284755 a(7) > 10^12. - _Giovanni Resta_, Apr 13 2017
%H A284755 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/RestrictedDivisorFunction.html">Restricted Divisor Function</a>
%H A284755 <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>
%t A284755 Select[Range[2, 1300000], Mod[Sum[DivisorSigma[1, k] - k, {k, 1, #}], Sum[DivisorSigma[0, k] - 1, {k, 1, #}]] == 0 &]
%Y A284755 Cf. A000005, A000203, A001065, A002541, A003601, A023884, A023886, A027751, A153485, A226647, A284288.
%K A284755 nonn,more
%O A284755 1,1
%A A284755 _Ilya Gutkovskiy_, Apr 02 2017