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 A115890 #14 Jul 15 2021 21:23:12 %S A115890 1,2,141,517,1089,1621,1651,2359,17529,20086,124282,1664338,72452549, %T A115890 1503846167,14457164981,17107594211,17458514913,24556027479 %N A115890 Numbers k such that k*sigma(k) is a palindrome. %C A115890 a(19) > 5*10^10. - _Donovan Johnson_, Jul 22 2011 %e A115890 1664338*sigma(1664338) = 1664338*2688588 = 4474719174744. %Y A115890 Cf. A084122, A115891, A115892. %K A115890 nonn,base,more %O A115890 1,2 %A A115890 _Giovanni Resta_, Feb 06 2006 %E A115890 a(13) from _Donovan Johnson_, Dec 02 2009 %E A115890 a(14)-a(18) from _Donovan Johnson_, Jul 22 2011