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 A141643 #25 Jun 06 2025 00:39:21 %S A141643 24,91963648,10200236032 %N A141643 Numbers k such that sigma(k)/k = 5/2. %C A141643 There are no other terms through 2^34. - _Walter Nissen_, Apr 17 2009 %C A141643 No more terms below 10^12. - _Jud McCranie_, Aug 30 2013 %C A141643 a(4) > 10^100 if it exists. - _Max Alekseyev_, Jun 05 2025 %H A141643 G. P. Michon, <a href="http://www.numericana.com/answer/numbers.htm#multiperfect">Multiperfect and hemiperfect numbers</a> %H A141643 Walter Nissen, <a href="http://upforthecount.com/math/abundance.html">Abundancy : Some Resources </a> %H A141643 Walter Nissen, <a href="http://upforthecount.com/math/abundance.html">Abundancy : Some Resources </a> %H A141643 Walter Nissen, <a href="http://upforthecount.com/math/ffp8.html">Primitive Friendly Pairs with friends < 2^34 with denom < 20000</a> %t A141643 Select[Range[100000], DivisorSigma[1, #]/# == 5/2 &] (* _Robert Price_, Apr 03 2019 *) %o A141643 (PARI) isok(k) = sigma(k, -1) == 5/2; \\ _Michel Marcus_, Apr 04 2019 %Y A141643 Cf. A055153, A141645, A159271, A160678. %K A141643 nonn,more,bref %O A141643 1,1 %A A141643 _Yasutoshi Kohmoto_, May 10 2008 %E A141643 Definition rewritten by _M. F. Hasler_, May 10 2008 %E A141643 First three terms confirmed by _Ray Chandler_, Sep 18 2008