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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
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OFFSET
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1,2
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COMMENTS
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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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LINKS
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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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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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