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 A046840 #29 Mar 17 2025 02:42:17
%S A046840 1,3,4,5,7,11,12,13,15,16,17,19,20,21,23,25,27,28,29,31,33,35,37,39,
%T A046840 41,43,44,47,48,49,51,52,53,55,57,59,60,61,65,67,68,69,71,73,75,76,77,
%U A046840 79,80,81,83,84,85,87,89,91,92,93,95,97,100,101,103,105,107,108,109,111
%N A046840 Numbers k such that the number of divisors of k divides the sum of the 4th powers of the divisors of k.
%C A046840 A020486 is very similar to this sequence, but it does not include the following values below 1000 (which this sequence does include): {16, 80, 81, 176, 304, 324, 400, 405, 464, 496, 656, 784, 880, 891, 944, 976}.
%H A046840 Amiram Eldar, <a href="/A046840/b046840.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from T. D. Noe)
%e A046840 k = 16 is a term since it has 5 divisors, and sigma_4(16) = 69905 is divisible by 5.
%t A046840 Select[Range[120], Divisible[DivisorSigma[4, #], DivisorSigma[0, #]] &] (* _Amiram Eldar_, Mar 17 2025 *)
%o A046840 (Magma) [n: n in [1..120] | IsZero(DivisorSigma(4, n) mod NumberOfDivisors(n))]; // _Bruno Berselli_, Apr 11 2013
%o A046840 (PARI) isok(n) = sigma(n, 4) % numdiv(n) == 0; \\ _Michel Marcus_, May 13 2018
%Y A046840 Cf. A000005, A001159.
%Y A046840 Cf. A003601, A020486, A046839.
%K A046840 nonn
%O A046840 1,2
%A A046840 _Labos Elemer_