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%I #19 Nov 02 2019 02:53:04
%S 9,999,99999,9999999,999969999,99999999999,9999998999999,
%T 999999999999999,99999999799999999,9999999997999999999,
%U 999999999999999999999,99999999999899999999999,9999999999999999999999999,999999999999979999999999999,99999999999999999999999999999,9999999999999996999999999999999
%N a(n) is the largest (2n+1)-digit palindrome that is the product of two numbers having an equal number of digits.
%C A308803 is the union of this sequence and A327897. This sequence lists the terms of odd indices of A308803 as they seem to be easier to compute than terms of even indices of A308803 (the sequence A327897).
%H Chai Wah Wu, <a href="/A327435/b327435.txt">Table of n, a(n) for n = 0..89</a>
%F a(n) = A308803(2n+1).
%F a(n) >= (2*10^n-1)(5*10^n+1) = 10^(2n+1)-3*10^n-1. If n is a term of A308983, then a(n) = 10^(2n+1)-3*10^n-1.
%e a(0) = 9 = 3 * 3
%e a(1) = 999 = 27 * 37
%e a(2) = 99999 = 123 * 813
%e a(3) = 9999999 = 2151 * 4649
%e a(4) = 999969999 = 16667 * 59997
%e a(5) = 99999999999 = 194841 * 513239
%e a(6) = 9999998999999 = 2893921 * 3455519
%e a(7) = 999999999999999 = 11099889 * 90090991
%e a(8) = 99999999799999999 = 265412903 * 376771433
%e a(9) = 9999999997999999999 = 2441330309 * 4096127411
%e a(10) = 999999999999999999999 = 19845575559 * 50389065161
%e a(11) = 99999999999899999999999 = 345867517613 * 289128047323
%Y Cf. A002113, A308803, A308983, A327897.
%K nonn,base
%O 0,1
%A _Chai Wah Wu_, Oct 03 2019