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Search: id:A085245
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| A085245 |
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Least k such that k*2^n + 1 is a semiprime. |
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2
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| 4, 2, 1, 2, 1, 1, 1, 6, 3, 2, 1, 1, 1, 6, 3, 2, 1, 2, 1, 1, 3, 2, 1, 3, 8, 4, 2, 1, 3, 2, 1, 1, 3, 7, 5, 5, 8, 4, 2, 1, 4, 2, 1, 3, 3, 7, 6, 3, 15, 9, 29, 28, 14, 7, 6, 3, 3, 8, 4, 2, 1, 4, 2, 1, 14, 7, 12, 6, 3, 3, 9, 5, 12, 6, 3, 8, 4, 2, 1, 3, 29, 18, 9, 18, 9, 10, 5, 13, 8, 4, 2, 1, 15, 12, 6, 3, 9, 6
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The first few values of n such that 78557*2^n + 1 is a semiprime, where k = 78557 (the conjectured smallest Sierpinski number), are: 2,3,7,15,17,18,24,60,71,89,92,107,140,143,163,... Conjecture: there are infinitely many semiprimes of this form.
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EXAMPLE
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a(51)=29 because k*2^51 + 1 is not a semiprime for k=1,2,...28, but
29*2^51 + 1 = 63839 * 1022920073887 is.
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CROSSREFS
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Cf. A001358, A035050, A076336.
Adjacent sequences: A085242 A085243 A085244 this_sequence A085246 A085247 A085248
Sequence in context: A016509 A010313 A075826 this_sequence A046096 A080816 A016507
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KEYWORD
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nonn
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), Aug 11 2003
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