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A332661 a(1)=1; a(n+1) is the smallest palindrome not already in the sequence such that the product of a(n+1) and a(n) is also a palindrome. 1
1, 2, 3, 11, 4, 22, 101, 5, 111, 6, 1001, 7, 88, 77, 8, 1111, 9, 10001, 33, 121, 131, 202, 44, 2002, 141, 212, 1221, 303, 2112, 222, 3003, 232, 10101, 55, 99, 555, 979, 5555, 9779, 55555, 97779, 100001, 66, 1000001, 151, 11011, 161, 11111, 171, 101101, 181 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

First mentioned by Eric Angelini in the 'math-fun' mailing list on Jan 12, 2020.

The sequence is infinite because, when all smaller numbers fail, a sufficiently large 10^k+1 will always succeed.

LINKS

Hans Havermann, Table of n, a(n) for n = 1..303

EXAMPLE

a(4) = 11 because because the smallest not-yet-used palindromes (4, 5, 6, 7, 8, 9) multiplied by 3 are not base-10 palindromes, but 11*3 is.

CROSSREFS

Cf. A002113 (base-10 palindromes).

Sequence in context: A046641 A083664 A083125 * A031335 A084743 A030391

Adjacent sequences:  A332657 A332658 A332659 * A332662 A332663 A332664

KEYWORD

nonn,base

AUTHOR

Eric Angelini and Hans Havermann, Feb 18 2020

STATUS

approved

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Last modified April 9 14:04 EDT 2020. Contains 333353 sequences. (Running on oeis4.)