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3, 7, 1, 1, 7, 1, 7, 7, 1, 1, 7, 1, 1, 1, 7, 7, 1, 7, 1, 7, 7, 7, 7, 1, 1, 7, 7, 7, 1, 1, 1, 7, 7, 1, 7, 1, 7, 7, 7, 7, 1, 1, 1, 7, 1, 7, 1, 7
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Aside from "3", all terms of A127928 must be 1 or 7 mod 18 (see A127928 for mod rules); but not all primes mod 1 or 7 are pure hailstone numbers. For example, the prime 61 == 7 mod 18 but 61 is impure. Conjecture: for large n, the numbers of 1 and 7 mod 18 terms are approximately equal.
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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
| Pure hailstone (Collatz) numbers that are also prime (i.e. the set A127928), mod 18.
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EXAMPLE
| a(5) = 7 since A127928(5) = 43 and 43 == 7 mod 18.
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CROSSREFS
| Cf. A127928, A127930, A061641, A127633, A006577, A066903.
Sequence in context: A072450 A085785 A200235 * A200922 A003118 A096409
Adjacent sequences: A127926 A127927 A127928 * A127930 A127931 A127932
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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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