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A085917
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Least k such that k*2^n - 1 is a semiprime.
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0
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5, 4, 2, 1, 3, 5, 4, 2, 1, 2, 1, 3, 6, 3, 3, 3, 3, 6, 3, 3, 3, 2, 1, 3, 6, 3, 6, 3, 6, 3, 3, 11, 16, 8, 4, 2, 1, 8, 4, 2, 1, 15, 13, 15, 16, 8, 4, 2, 1, 6, 3, 17, 15, 12, 6, 3, 4, 2, 1, 3, 6, 3, 3, 5, 3, 2, 1, 5, 6, 3, 48, 24, 12, 6, 3, 12, 6, 3, 10, 5, 4, 2, 1, 3, 3, 31, 21, 17, 15, 11, 13, 24, 12, 6, 3
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The first few values of n such that 509203*2^n - 1 is a semiprime, where k = 509203 (the conjectured smallest Riesel number), are: 3,4,16,34,61,82,124,142,163,171,... Conjecture: there are infinitely many semiprimes of this form.
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EXAMPLE
| a(33)=16 because k*2^33 - 1 is not a semiprime for k=1,2,...15, but 16*2^33 - 1 = 223 * 616318177 is.
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CROSSREFS
| Cf. A001358, A085427, A076337, A085245.
Sequence in context: A102220 A201680 A109430 * A180130 A102593 A090462
Adjacent sequences: A085914 A085915 A085916 * A085918 A085919 A085920
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KEYWORD
| nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Aug 16 2003
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