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A037084 Positive integers not going to 1 under iterations of the map in A001281: n->3n-1 if n odd, n->n/2 if n even. +0
12
5, 7, 9, 10, 13, 14, 17, 18, 19, 20, 21, 23, 25, 26, 27, 28, 31, 33, 34, 35, 36, 37, 38, 40, 41, 42, 45, 46, 47, 49, 50, 51, 52, 54, 55, 56, 61, 62, 63, 66, 67, 68, 70, 72, 73, 74, 75, 76, 80, 81, 82, 83, 84, 89, 90, 91, 92, 93, 94, 98, 99, 100, 102 (list; graph; listen)
OFFSET

1,1

COMMENT

Up to at least 100000000, every number reaches 1, 5 or 17.

Conjecture : for any x, the iterated process "x ->3x-1" if x is odd or "x ->x/2" if x is even leads to one of the following three cycles: (1, 2), (5, 14, 7, 20, 10), (41, 122, 61, 182, 91, 272, 136, 68, 34, 17, 50, 25, 74, 37, 110, 55, 164, 82). - Benoit Cloitre (benoit7848c(AT)orange.fr), May 14 2002

Complement (in N*) of A039500 ; union of A039501 and A039502 (conjectured). - M. F. Hasler, Nov 26 2007

EXAMPLE

Iterations of f starting at 3 are 3,8,4,2,1 - thus 3 is not in the sequence. Iterations starting at 5 are 5,14,7,20,10,5 -periodic, and 1 is not among these values, so 5 is in the sequence.

PROGRAM

(PARI) A037084( end=999, n=0 /*starting value -1 */)={ for( i=n, end, n=i; while( n > 17 | n > 5 & n < 17, if( n%2, n=3*n-1, n>>=1)); if( n > 4, print1(i", ")))} \\ - M. F. Hasler, Nov 26 2007

CROSSREFS

Cf. A001281, A039500-A039505.

Cf. A006370, A006577 (Collatz problem: 3n+1).

Sequence in context: A129270 A138892 A005523 this_sequence A018935 A039501 A114255

Adjacent sequences: A037081 A037082 A037083 this_sequence A037085 A037086 A037087

KEYWORD

nonn,easy

AUTHOR

Robert W. Craigen (craigen(AT)fresno.edu)

EXTENSIONS

More terms from Christian G. Bower (bowerc(AT)usa.net), Feb 15 1999.

Edited by M. F. Hasler (maximilian.hasler(AT)gmail.com), Nov 26 2007.

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Last modified July 25 07:41 EDT 2008. Contains 142293 sequences.


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