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 A226647 #28 Apr 03 2023 10:36:13
%S A226647 1,9,25,37,63,71876888199
%N A226647 Numbers k such that Sum_{i=1..k} sigma(i) is divisible by Sum_{i=1..k} d(i), where sigma(i) = sum of divisors of i (A000203), and d(i) = number of divisors of i (A000005).
%C A226647 No other terms below 2^36. - _Alex Ratushnyak_, Jun 29 2013
%C A226647 The ratio corresponding to a(6) is 4249100789716352394810 / 1807894350282 = 2350303705. a(7) > 10^12. - _Giovanni Resta_, Apr 13 2017
%H A226647 C. K. Caldwell, and G. L. Honaker, Jr., <a href="https://t5k.org/curios/page.php?curio_id=29587">Prime curio for 37</a>
%F A226647 Numbers k such that A006218(k) divides A024916(k).
%e A226647 A006218(9) = 23, A024916(9) = 69, 23 divides 69, so 9 is in the sequence.
%t A226647 Flatten[Position[Accumulate[Table[{DivisorSigma[1,n],DivisorSigma[0,n]},{n,100}]],_?(Divisible[First[#],Last[#]]&),{1},Heads->False]] (* _Harvey P. Dale_, Jun 19 2013 *)
%o A226647 (PARI) isok(n) = sum(k=1, n, sigma(k)) % sum(k=1, n, numdiv(k)) == 0; \\ _Michel Marcus_, Jul 07 2016
%Y A226647 Cf. A000005, A000203, A006218, A024916.
%K A226647 nonn,more
%O A226647 1,2
%A A226647 _Alex Ratushnyak_, Jun 13 2013
%E A226647 a(6) from _Giovanni Resta_, Apr 12 2017