

A146169


Percentage (rounded) of semiprimes <= 2^n which are odd and squarefree.


0



0, 0, 17, 20, 36, 48, 56, 61, 65, 69, 71, 73, 75, 76, 77, 78, 79, 80, 80, 81, 81, 82, 82, 82, 83, 83, 83, 83, 84, 84, 84, 84
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OFFSET

2,3


COMMENTS

More than 84% of the semiprimes in the interval [4, 2^32] are odd and squarefree. This percentage appears to rise indefinitely as n grows.


LINKS



FORMULA



EXAMPLE

a(5)= 20 since the interval [4, 2^5] contains 10 semiprimes, namely 4,6,9,10,14,15,21,22,25 and 26; and two of those semiprimes, (15 and 21), are odd and squarefree.


PROG

(PARI) a(n)=my(s, i, N=2^n); forprime(p=2, sqrtint(N), s+=primepi(N\p); i++); s=i*(i1)/2; i=primepi(sqrtint(N))+primepi(N/2)1; round(100*(si)/s) \\ Charles R Greathouse IV, May 12 2013


CROSSREFS

Cf. A001358(semiprimes), A125527(Number of semiprimes <= 2^n), A146168(Number of odd squarefree semiprimes < 2^n).


KEYWORD

nonn


AUTHOR



STATUS

approved



