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A072122 Numbers with 12 odd integers in their Collatz (or 3x+1) trajectory. 1
39, 78, 79, 153, 156, 157, 158, 305, 306, 307, 312, 314, 315, 316, 317, 610, 611, 612, 613, 614, 624, 628, 629, 630, 631, 632, 634, 647, 683, 687, 1220, 1221, 1222, 1224, 1226, 1228, 1229, 1241, 1248, 1256, 1257, 1258, 1260, 1261, 1262, 1264, 1265, 1268 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The Collatz (or 3x+1) function is f(x) = x/2 if x is even, 3x+1 if x is odd. The Collatz trajectory of n is obtained by applying f repeatedly to n until 1 is reached.

REFERENCES

J. Shallit and D. Wilson, The "3x+1" Problem and Finite Automata, Bulletin of the EATCS #46 (1992) pp. 182-185.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

J. Shallit and D. Wilson, The "3x+1" Problem and Finite Automata, Bulletin of the EATCS #46 (1992) pp. 182-185.

Index entries for 2-automatic sequences.

EXAMPLE

trajectory: 39, 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 has 12 odd numbers.

MATHEMATICA

odd12Q[n_]:=Count[NestWhileList[If[EvenQ[#], #/2, 3#+1]&, n, #>1&], _?OddQ]==12; Select[Range[1300], odd12Q] (* Harvey P. Dale, Oct 17 2011 *)

CROSSREFS

Cf. A062052-A062060.

Sequence in context: A253153 A044105 A044486 * A290815 A063335 A020264

Adjacent sequences:  A072119 A072120 A072121 * A072123 A072124 A072125

KEYWORD

easy,nonn

AUTHOR

Jim Nastos, Jun 19 2002

STATUS

approved

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Last modified September 23 22:32 EDT 2020. Contains 337315 sequences. (Running on oeis4.)