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 A196509 #17 Aug 13 2020 14:02:28 %S A196509 9,11,343,747,6556,65856,405504,4251524,8847488 %N A196509 Largest palindrome formed by using n single-digit numbers and the operators +, -, * and / where concatenation is not allowed. %C A196509 This puzzle is easily trivial if exponentiation or concatenation is allowed. %C A196509 Best known results for a(10)..a(15) are 88499488, 846747648, 4095995904, 23613431632, 68899199886, 633498894336. %C A196509 Erich Friedman solved and proved most of these terms. %H A196509 Erich Friedman, <a href="https://erich-friedman.github.io/mathmagic/0699.html">Problem of the month June 1999</a> %e A196509 11 = 9 + 2 %e A196509 343 = 7 * 7 * 7 %e A196509 747 = 9 * (9 * 9 + 2) %e A196509 6556 = 9 * 9 * 9 * 9 - 5 %e A196509 65856 = 3 * 7 * 7 * 8 * 8 * 8 %e A196509 405504 = 8 * 8 * 8 * 8 * 9 * (9 + 2) %e A196509 4251524 = 8 * 9 * 9 * 9 * 9 * 9 * 9 - 4 %e A196509 8847488 = 8 * 8 * (5 * 6 * 8 * 8 * 8 * 9 + 2) %Y A196509 Cf. A002113. %K A196509 nonn,base,more %O A196509 1,1 %A A196509 _Kausthub Gudipati_, Oct 03 2011