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Search: id:A070991
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| A070991 |
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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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| 2, 3, 5, 6, 9, 11, 14, 17, 18, 39, 41, 47, 54, 57, 59, 62, 71, 81, 89, 107, 108, 161, 252, 284, 378, 639, 651, 959, 977, 1368, 1439, 1823, 2159, 2430, 2735, 3239, 4103, 4617, 4859, 6155, 7289, 9233
(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?
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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) and 39-1=38 is reached, hence 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, print1(n, ", "); ); ))
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CROSSREFS
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Sequence in context: A104214 A046657 A102825 this_sequence A008747 A054639 A070757
Adjacent sequences: A070988 A070989 A070990 this_sequence A070992 A070993 A070994
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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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