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 A046871 #34 Jun 15 2024 05:48:35 %S A046871 1,4,9,16,20,25,36,48,49,64,81,100,121,144,162,169,180,196,225,245, %T A046871 256,289,324,361,400,432,441,484,500,529,576,605,625,648,676,729,784, %U A046871 841,900,931,961,980,1024,1089,1156,1200,1225,1280,1296,1369,1444,1521 %N A046871 Numbers k such that sigma_2(k) divides sigma_4(k). %C A046871 sigma_2(k) is the sum of the squares of the divisors of k (A001157). %C A046871 sigma_4(k) is the sum of the 4th powers of the divisors of k (A001159). %H A046871 Amiram Eldar, <a href="/A046871/b046871.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Paolo P. Lava) %e A046871 k = a(8) = 48 of which divisor power sums for powers 0, 1, 2, 3, 4 are 10, 124, 3410, 131068, 5732210, respectively. Here sigma_2(k) = 3410 and sigma_4(k) = 3410*1681. %t A046871 Select[Range@ 1600, Divisible[DivisorSigma[4, #], DivisorSigma[2, #]] &] (* _Michael De Vlieger_, May 20 2017 *) %o A046871 (Magma) [n: n in [1..1600] | IsZero(DivisorSigma(4,n) mod DivisorSigma(2,n))]; // _Bruno Berselli_, Apr 10 2013 %o A046871 (PARI) isok(n) = !(sigma(n, 4) % sigma(n, 2)); \\ _Michel Marcus_, May 21 2017 %Y A046871 Cf. A001157, A001159, A020487, A020486, A046841. %K A046871 nonn %O A046871 1,2 %A A046871 _Labos Elemer_