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%I #20 May 13 2019 13:46:43
%S 1,3,9,111,333,999,12321,36963,1001001,3003003,9009009,111111111,
%T 333333333,999999999,12333333321,36999999963,1002003002001,
%U 3006009006003,111222333222111,333666999666333,12345678987654321
%N The 21 palindromic divisors of the palindrome 12345678987654321.
%C There are 45 divisors of 12345678987654321.
%C Motivated by A261072 by _Ilya Gutkovskiy_, which has only six palindromic divisors, namely 1, 3, 7, 9, 171, 1234567890987654321.
%C 12345678987654321 = A002275(9)^2 = 111111111^2 (observed by _Jon E. Schoenfield_). The repunit R(9) has the eight palindromic divisors 1, 3, 9, 111, 333, 1001001, 3003003, 111111111.
%C All entries a(n) can be obtained by multiplying two palindromic divisors of R(9).
%t Select[Divisors[12345678987654321],PalindromeQ] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, May 13 2019 *)
%Y Cf. A002275, A261072.
%K nonn,easy,base,fini,full
%O 1,2
%A _Wolfdieter Lang_, Aug 22 2015
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