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