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 A070993 Numbers n such that the trajectory of n under the "3x+1" map reaches n+1. 6
 3, 7, 9, 15, 19, 25, 33, 39, 51, 91, 121, 159, 166, 183, 243, 250, 333, 376, 411, 432, 487, 501, 649, 667, 865, 889, 975, 1153, 1185, 1299, 1335, 1731, 1779, 2307, 3643, 4857, 7287 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS From Collatz conjecture, the trajectory of n never reaches n again. Is this sequence finite? (it seems there are no further terms below 10^6). There are no more terms < 10^9. - Donovan Johnson, Sep 22 2013 LINKS Table of n, a(n) for n=1..37. EXAMPLE Trajectory of 39 is (118, 59, 178, 89, 268, 134, 67, 202, 101, 304, 152, 76, 38, 19, 58, 29, 88, 44, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1) which contains 39+1=40, so 39 is in the sequence. MATHEMATICA Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; Select[Range[100000], MemberQ[Collatz[#], # + 1] &] (* T. D. Noe, Feb 22 2013 *) PROG (PARI) for(n=1, 10000, s=n; t=0; while(s!=1, t++; if(s%2==0, s=s/2, s=3*s+1); if(s==n-1, print1(n, ", "); ); )) CROSSREFS Cf. A070165 (Collatz trajectories), A221213, A222293, A070991. Sequence in context: A104177 A099204 A219608 * A261524 A261871 A191131 Adjacent sequences: A070990 A070991 A070992 * A070994 A070995 A070996 KEYWORD nonn AUTHOR Benoit Cloitre and Boris Gourevitch (boris(AT)pi314.net), May 18 2002 EXTENSIONS Corrected by T. D. Noe, Oct 25 2006 STATUS approved

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Last modified June 3 14:22 EDT 2023. Contains 363112 sequences. (Running on oeis4.)