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 A008920 #30 Nov 20 2021 21:27:18 %S A008920 0,18,99,198,261,342,423,504,585,666,747,828,909,1089,1170,1251,1332, %T A008920 1413,1494,1575,1656,1737,1818,1881,1998,2772,2871,3663,3762,4554, %U A008920 4653,5445,5544,6336,6435,7227,7326,8118,8217,9009,9108,9999,10890,10989,11781 %N A008920 Let j = | i - i_written_backwards |, k = j + j_written_backwards; then k is in this sequence. %C A008920 There were originally some terms missing from this sequence, for example 909 generated from 101001. It seems likely to me that Conway only checked generators up to 100000. It's possible to prove that there are now no missing terms of the sequence by noting that if an n-digit number is not a palindrome then the difference between it and its reversal is at least 9*10^(n/2 - 1). - _Oscar Cunningham_, Sep 10 2021 %D A008920 J. H. Conway, personal communication. %H A008920 Oscar Cunningham, <a href="/A008920/b008920.txt">Table of n, a(n) for n = 1..30484</a> %Y A008920 Cf. A004086, A335978. %K A008920 nonn,base %O A008920 1,2 %A A008920 _N. J. A. Sloane_ and _J. H. Conway_ %E A008920 Offset 1 and missing terms added by _Oscar Cunningham_, Sep 10 2021