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OFFSET
| 1,1
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COMMENTS
| Through a(9) the terms have the following number of 3x+1 problem steps: 7, 29, 113, 23, 37, 53, 43, 131, 173.
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REFERENCES
| Douglas J. Shaw, "The Pure Numbers Generated by the Collatz Sequence", Fibonacci Quarterly, August, 2006; p. 201.
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FORMULA
| A127928 = numbers that are both pure hailstone (Collatz) and prime. A127930 = the subset having prime steps to reach 1; given the Collatz rule C(n) = {3n+1, n odd; n/2 if n is even}.
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EXAMPLE
| 3 is in the set A127930 since the iterative trajectory of 3 has 7 steps: (10, 5, 16, 8, 4, 2, 1) and 7 is prime.
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CROSSREFS
| Cf. A006577, A066903, A127928, A127928, A061641, A127633.
Sequence in context: A142184 A199348 A002551 * A062647 A003525 A042661
Adjacent sequences: A127927 A127928 A127929 * A127931 A127932 A127933
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KEYWORD
| nonn
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AUTHOR
| Gary W. Adamson (qntmpkt(AT)yahoo.com), Feb 07 2007
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