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A117817 Let T_n be the infinite sequence formed by starting with 1 and repeatedly reversing the digits and adding n to get the next term. If T_n eventually reaches a cycle, sequence gives length of that cycle, otherwise -1. 72

%I

%S 9,81,3,54,207,30,63,27,1,-1,9,15,18,72,-1,90,54,13,18,-1,15,9,9,36,

%T 45,18,9,36,18,-1,9,9,3,36,72,2,27,18,3,-1,18,57,63,9,22,90,18,30,54,

%U -1,6,99,54,13,36,207,12,63,45,-1,36,27,30,108,36,264,99,36,3,-1,18,22,45,90,12,45,117,192,18,-1,36,45,63,168,1008,36,24,306,9,-1,99,639,36,54,144,18,225,468,1,-1,18,300,189,171,765,90,45,462,90,-1,9,513,63,69

%N Let T_n be the infinite sequence formed by starting with 1 and repeatedly reversing the digits and adding n to get the next term. If T_n eventually reaches a cycle, sequence gives length of that cycle, otherwise -1.

%C a(multiple of 10) = -1 (see A117816). a(15) = -1 (see A118532). a(n) is a multiple of 9/gcd(9,n) unless it is -1. - _Martin Fuller_, May 12 2006

%C For a discussion of the -1 entries see A117816.

%H N. J. A. Sloane and others, <a href="/wiki/Sequences_of_RADD_type">Sequences of RADD type</a>, OEIS wiki.

%t ReverseNum[n_] := FromDigits[Reverse[IntegerDigits[n]]]; maxLen=10000; Table[z=1; lst={1}; While[z=ReverseNum[z]+n; !MemberQ[lst,z] && Length[lst]<maxLen, AppendTo[lst,z]]; If[Length[lst]<maxLen, Length[lst]-Position[lst,z][[1,1]]+1, -1], {n,100}] (Noe)

%Y See A117817 for the -1 entries and cross-references to T_1 through T_16.

%K sign,base

%O 1,1

%A _N. J. A. Sloane_, following discussions with Luc Stevens, May 04 2006

%E a(21)-a(33) from Luc Stevens, May 08 2006

%E a(33) onwards from _T. D. Noe_ and _Martin Fuller_, May 10 2006

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Last modified August 15 13:27 EDT 2020. Contains 336504 sequences. (Running on oeis4.)