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 A002069 M3924 N1612 #33 Apr 15 2025 17:23:31 %S A002069 0,1,5,22,1001,2882,15251,720027,7081807,7451547,26811862,54177145, %T A002069 1050660501,1085885801,1528888251,2911771192,2376574756732, %U A002069 5792526252975,5875432345785,10810300301801,264571020175462,5292834004382925,10808388588380801,15017579397571051 %N A002069 Palindromic pentagonal numbers. %D A002069 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). %D A002069 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A002069 Bert Dobbelaere, <a href="/A002069/b002069.txt">Table of n, a(n) for n = 1..58</a> (terms 1..22 from N. J. A. Sloane, terms 23..30 from Robert Price) %H A002069 Patrick De Geest, <a href="https://www.worldofnumbers.com/penta.htm">More about Palindromic Pentagonals</a> %H A002069 A. Gloden and R. A. Johnson, <a href="http://www.jstor.org/stable/2304262">Problem E427</a>, Amer. Math. Monthly, 48 (1941), 211-212. %t A002069 Select[PolygonalNumber[5,Range[0,6*10^7]],PalindromeQ] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jan 15 2018 *) %Y A002069 Cf. A028386, A000326. %K A002069 nonn,base %O A002069 1,3 %A A002069 _N. J. A. Sloane_