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Search: id:A111067
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| A111067 |
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Number of odd primes p < 10^n such that p+2=product of 2 primes (no twin Chen primes). |
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+0
1
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| 1, 11, 79, 427, 3009, 21779, 166649, 1322266, 10752066
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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A006880(n)=number of primes < 10^n, A007508(n)=number of twin primes < 10^n. Let F(n) = A006880(n)/A007508(n). For n >3, we find that F(n) is ~ 0.762373*log(10^n) - 0.968855.
Let FF(n) = A006880(n)/a(n). For n>3, we find that FF(n) is ~ 0.163128*log(10^n) + 1.349255. a(n)/A007508(n) is then ~ 0.762373*log((10^n) - 0.968855 / ( 0.163128*log(10^n) + 1.349255, as n tends to infinity a(n)/ A007508(n) needs to tend to 0.762373 / 0.163128 = 4.673465.
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EXAMPLE
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7 is the only prime <10 with 7+2=3*3=product of 2 odd primes so a(1)=1.
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CROSSREFS
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Cf. A006880, A007508.
Sequence in context: A140542 A101983 A139953 this_sequence A026841 A026848 A026864
Adjacent sequences: A111064 A111065 A111066 this_sequence A111068 A111069 A111070
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KEYWORD
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nonn
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AUTHOR
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Pierre CAMI (pierrecami(AT)tele2.fr), Oct 08 2005
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EXTENSIONS
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a(8) corrected and a(9) computed by Robert G. Wilson v (rgwv(at)rgwv.com), Oct 10 2005
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