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 A090777 #14 May 09 2022 08:37:58 %S A090777 1,6,28,120,364,496,672,840,1080,1488,1782,2280,3276,3472,7440,8128, %T A090777 8736,11880,12400,18360,20832,24384,25296,26208,30240,30256,32760, %U A090777 35640,37200,56896,57240,84360,86800,90768,115560,121920,131040,149856,170688 %N A090777 Numbers k such that sigma(k) divides k^2. %H A090777 Donovan Johnson, <a href="/A090777/b090777.txt">Table of n, a(n) for n = 1..1000</a> %t A090777 Select[Range[200000], Divisible[#^2, DivisorSigma[1, #]] &] (* _Amiram Eldar_, May 09 2022 *) %o A090777 (PARI) for (n=1,10^6, if ( n^2 % sigma(n) ==0, print1(n,", "))); /* _Joerg Arndt_, May 28 2012 */ %Y A090777 Cf. A000203, A000290. %K A090777 nonn %O A090777 1,2 %A A090777 _Benoit Cloitre_, Feb 08 2004