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A072719
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Numbers n such that 17 applications of 'Reverse and Subtract' lead to n, whereas less than 17 applications do not lead to n.
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7
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1186781188132188, 1464465185355348, 2178772178212278, 2191191178088088, 2196702178032978, 2202202177977978, 2334334176656658, 3041250269587497, 4361064356389356, 4906609350933906, 6232232537677674, 6543356534566434
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| There are 17 sixteen-digit terms in the sequence. Further terms are obtained (a) by inserting at the center of these terms any number of 9's and (b) by concatenating a term any number of times with itself and inserting an equal number of 0's at all junctures. Method (b) may be applied recursively to all terms. - Revised thanks to a comment from Hans Havermann, Jan 27 2004.
This is a working sequence. It is neither by computation nor by proof guaranteed that there are no smaller or interleaved terms.
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FORMULA
| n = f^17(n), n <> f^k(n) for k < 17, where f: x -> |x - reverse(x)|.
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EXAMPLE
| 1186781188132188 -> 7625537623744623 -> 4361064356389356 -> 2178772178212278 -> 6543356534566434 -> 2196702178032978 -> 6595606534043934 -> 2202202177977978 -> 6595595534044044 -> 2191191178088088 -> 6617617533823824 -> 2334334176656658 ->
6232232537677674 -> 1464465185355348 -> 6971070630289293 -> 3041250269587497 -> 4906609350933906 -> 1186781188132188.
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CROSSREFS
| Cf. A072137, A072141, A072142, A072143, A072718.
Sequence in context: A052098 A172607 A095431 * A185433 A134692 A098099
Adjacent sequences: A072716 A072717 A072718 * A072720 A072721 A072722
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KEYWORD
| base,nonn
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AUTHOR
| Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Jul 15 2002
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