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 A281507 #29 May 24 2022 00:11:37 %S A281507 1186061987030929990,2185352294922536801,3271704589845072613, %T A281507 6434410079699144336,12768830049399288682,41457129443403175403, %U A281507 71914259877895350817,143719619755790592734,581014717313707510075,1151030424627424920260,1771324671891665221771 %N A281507 Trajectory of 1186061987030929990 under the "Reverse and Add!" operation. %C A281507 1186061987030929990 is the largest of the first 126 numbers that require exactly 261 steps to turn into a palindrome (see A281506). The sequence reaches a 119-digit palindrome after 261 steps (see b-file). The number was obtained empirically using computer algorithms and was not reported before. %D A281507 Popular Computing (Calabasas, CA), The 196 Problem, Vol. 3 (No. 30, Sep 1975). %H A281507 Sergei D. Shchebetov, <a href="/A281507/b281507.txt">Table of n, a(n) for n = 0..261</a> %H A281507 Jason Doucette, <a href="http://jasondoucette.com/worldrecords.html">World Records</a> %H A281507 Yutaka Nishiyama, <a href="http://www.ijpam.eu/contents/2012-80-3/9/index.html">Numerical Palindromes and the 196 Problem</a>, International Journal of Pure and Applied Mathematics, Volume 80 No. 3 2012, 375-384. %H A281507 R. Styer, <a href="http://www41.homepage.villanova.edu/robert.styer/PalindromePaper1986.pdf">The Palindromic Conjecture and the Fibonacci Sequence</a>, Villanova University, 1986, 1-11. %H A281507 C. W. Trigg, <a href="http://www.jstor.org/stable/2689178">Palindromes by Addition</a>, Mathematics Magazine, 40 (1967), 26-28. %H A281507 C. W. Trigg, <a href="http://www.jstor.org/stable/2688651">More on Palindromes by Reversal-Addition</a>, Mathematics Magazine, 45 (1972), 184-186. %H A281507 Wikipedia, <a href="https://en.wikipedia.org/wiki/Lychrel_number">Lychrel Number</a> %H A281507 196 and Other Lychrel Numbers, <a href="http://www.p196.org/">196 and Lychrel Number</a> %H A281507 <a href="https://oeis.org/index/Res#RAA">Index entries for sequences related to Reverse and Add!</a> %F A281507 a(n+1) = a(n) + rev(a(n)). %e A281507 a(1) = 1186061987030929990 + 999290307891606811 = 2185352294922536801. %t A281507 NestList[#+IntegerReverse[#]&,1186061987030929990,20] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jan 17 2019 *) %o A281507 (Magma) k:=1186061987030929990; [n eq 1 select k else Self(n-1) + Seqint(Reverse(Intseq(Self(n-1)))): n in [1..20]]; // _Bruno Berselli_, Jan 23 2017 %Y A281507 Cf. A023109, A033672, A065198, A065199, A065320, A065321, A065322, A065323, A065324, A065325, A065326, A065327, A070743, A072216, A072217, A072218, A281301, A281390, A281506. %K A281507 nonn,base %O A281507 0,1 %A A281507 Andrey S. Shchebetov and _Sergei D. Shchebetov_, Jan 23 2017