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 A261245 The 21 palindromic divisors of the palindrome 12345678987654321. 1
 1, 3, 9, 111, 333, 999, 12321, 36963, 1001001, 3003003, 9009009, 111111111, 333333333, 999999999, 12333333321, 36999999963, 1002003002001, 3006009006003, 111222333222111, 333666999666333, 12345678987654321 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS There are 45 divisors of 12345678987654321. Motivated by A261072 by Ilya Gutkovskiy, which has only six palindromic divisors, namely 1, 3, 7, 9, 171, 1234567890987654321. 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. All entries a(n) can be obtained by multiplying two palindromic divisors of R(9). LINKS Table of n, a(n) for n=1..21. MATHEMATICA Select[Divisors[12345678987654321], PalindromeQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 13 2019 *) CROSSREFS Cf. A002275, A261072. Sequence in context: A053914 A018757 A281070 * A177243 A127100 A177793 Adjacent sequences: A261242 A261243 A261244 * A261246 A261247 A261248 KEYWORD nonn,easy,base,fini,full AUTHOR Wolfdieter Lang, Aug 22 2015 STATUS approved

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Last modified March 2 01:29 EST 2024. Contains 370447 sequences. (Running on oeis4.)