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 A111067 Number of odd primes p < 10^n such that p+2=product of 2 primes (no twin Chen primes). 0
 1, 11, 79, 427, 3009, 21779, 166649, 1322266, 10752066 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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. LINKS EXAMPLE 7 is the only prime <10 with 7+2=3*3=product of 2 odd primes so a(1)=1. CROSSREFS Cf. A006880, A007508. Sequence in context: A140542 A101983 A139953 * A172067 A026841 A026848 Adjacent sequences:  A111064 A111065 A111066 * A111068 A111069 A111070 KEYWORD nonn AUTHOR Pierre CAMI, Oct 08 2005 EXTENSIONS a(8) corrected and a(9) computed by Robert G. Wilson v, Oct 10 2005 STATUS approved

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Last modified January 20 14:47 EST 2021. Contains 340302 sequences. (Running on oeis4.)