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Search: id:A070993
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| A070993 |
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Numbers n such that the trajectory of n under the "3x+1" map reaches n+1. |
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+0
1
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| 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; listen)
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OFFSET
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1,1
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COMMENT
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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).
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EXAMPLE
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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.
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PROGRAM
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(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, pri nt1(n, ", "); ); ))
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CROSSREFS
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Sequence in context: A119681 A104177 A099204 this_sequence A128539 A057463 A118258
Adjacent sequences: A070990 A070991 A070992 this_sequence A070994 A070995 A070996
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre and Boris Gourevitch (benoit7848c(AT)orange.fr) (boris(AT)pi314.net), May 18 2002
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EXTENSIONS
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Corrected by T. D. Noe (noe(AT)sspectra.com), Oct 25 2006
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