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 A072139 Last term of the preperiodic part of the 'Reverse and Subtract' trajectory of n, or -1 if the trajectory is completely periodic. 2
 -1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 11, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 22, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 33, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 44, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 55, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 66, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 77, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 88, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 99, 99, 101, 99 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS 'Reverse and Subtract' (cf. A072137) is defined by x -> |x - reverse(x)|. For small n the positive terms are the first palindrome in the trajectory of n, so this sequence is a weak analog of A033865, which uses 'Reverse and Add'. a(1012) = 8712 is the first non-palindrome (cf. A072140). For k in A072140, A072141 or A072142 we have a(k) = -1. LINKS EXAMPLE a(0) = -1, since 0 -> |0 - 0| = 0, the preperiodic part is empty; a(12) = 9, since 12 -> |12 - 21| = 9. CROSSREFS Cf. A033865, A072137, A072140, A072141, A072142. Sequence in context: A081600 A239092 A017884 * A266325 A262087 A261914 Adjacent sequences:  A072136 A072137 A072138 * A072140 A072141 A072142 KEYWORD base,easy,sign AUTHOR Klaus Brockhaus, Jun 24 2002 STATUS approved

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Last modified September 19 09:35 EDT 2021. Contains 347556 sequences. (Running on oeis4.)