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 A115891 #9 Jul 15 2021 21:23:20 %S A115891 1,2,3,4,17,21,206,296,309,314,392,412,444,3016,3074,3182,3552,3632, %T A115891 4944,12998,52009,296448,2306507,2343809,2958948,3842106,4419666, %U A115891 14697047,15137567,21150749,25829523,29916818,41798278,157946358,215882549,318635303,442991424 %N A115891 Numbers k such that k times phi(k) is a palindrome. %e A115891 25829523 * phi(25829523) = 25829523 * 17219628 = 444774777477444. %Y A115891 Cf. A084122, A115890, A115892. %K A115891 nonn,base %O A115891 1,2 %A A115891 _Giovanni Resta_, Feb 06 2006 %E A115891 a(34)-a(37) from _Donovan Johnson_, Feb 17 2013