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Search: id:A009190
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| A009190 |
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2p twin peaks: a(n) = least x with lpf(x) = p(n) and lpf(y) < p(n) for all x < y < x + 2p(n). (p(n) = n-th prime, lpf(x) = least prime factor of x). |
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2
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| 7310131732015251470110369, 2061519317176132799110061, 3756800873017263196139951, 6316254452384500173544921
(list; graph; listen)
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OFFSET
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20,1
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COMMENT
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For prime p, a 2p-twin peak is a number x such that lpf(x) = lpf(x+2p) = p and x < y < x+2p => lpf(y) < p. (lpf(n) = least prime factor of n). p = 71 is the smallest prime admitting a 2p-twin peak.
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REFERENCES
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Various postings to math-fun mailing list, 1996-1997.
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LINKS
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Eric Weisstein's World of Mathematics, For more info
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CROSSREFS
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lpf(n) = A020639(n)
Sequence in context: A030198 A104267 A113538 this_sequence A095444 A133849 A095446
Adjacent sequences: A009187 A009188 A009189 this_sequence A009191 A009192 A009193
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KEYWORD
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nonn
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AUTHOR
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David W. Wilson (davidwwilson(AT)comcast.net)
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