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Search: id:A069577
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| A069577 |
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Smallest prime p such that pi(n) <= pi(p)*2, where pi(n) is the number of primes <= n, A000720. |
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+0
1
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| 2, 2, 2, 3, 3, 3, 3, 3, 3, 5, 5, 5, 5, 5, 5, 7, 7, 7, 7, 7, 7, 11, 11, 11, 11, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 17, 17, 17, 17, 17, 17, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 23, 23, 23, 23, 23, 23, 23, 23, 29, 29
(list; graph; listen)
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OFFSET
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2,1
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COMMENT
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a(n) separates the primes <= n in two sets {q<=a(n)} and {q<a(n)<=n} which differ in size by not more than 1.
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EXAMPLE
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Primes <= 20: {2,3,5,7,11,13,17,19}, therefore pi(20)=8 and from 8<=pi(7)*2=4*2 follows a(20)=7.
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CROSSREFS
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Cf. A007917, A000720, A000040.
Adjacent sequences: A069574 A069575 A069576 this_sequence A069578 A069579 A069580
Sequence in context: A070564 A072358 A074795 this_sequence A130239 A091092 A083375
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 18 2002
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