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 A344347 #18 Jun 12 2021 22:40:56 %S A344347 2,3,5,10,33,55,82,129,136,145,261,351,385,406,442,513,649,897,1090, %T A344347 2241,4726,5185,8650,13601,17101,17641,18241,26625,26937,29697,29953, %U A344347 32896,34561,35841,38417,44955,46081,46593,51985,63505,65703,66249,84376,93313,97903 %N A344347 Numbers k such that sigma(k)^2 is divisible by k-1. %e A344347 For k=10, sigma(10)^2 / (10-1) = 18^2 / 9 = 324 / 9 = 36. %t A344347 Select[Range[2, 10^5], Divisible[DivisorSigma[1, #]^2, # - 1] &] (* _Amiram Eldar_, May 15 2021 *) %o A344347 (PARI) %o A344347 list(nn) = for(n=2, nn, if (sigma(n)^2 % (n-1) == 0, print1(n, ", "))) %o A344347 list(100000) %Y A344347 Cf. A072861, A263928. %K A344347 nonn %O A344347 1,1 %A A344347 _Zdenek Cervenka_, May 15 2021