OFFSET

1,2

COMMENTS

One can prove that non-semiprimes we can find among preprimes of the n-th kind only with the smallest prime divisor 2,3,...,prime(n), where n=1 corresponds to A156759, n=2 corresponds to A247393, n=3 corresponds to A247394, etc. For example, for n=1, only among even numbers of A156759; for n=2 - only among even numbers and numbers with the smallest prime divisor 3 of A247393, etc. Thus, for every n>=1, among preprimes of the n-th kind almost all numbers are semiprimes.

LINKS

CROSSREFS

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Sep 22 2014

EXTENSIONS

More terms from Peter J. C. Moses, Sep 22 2014

STATUS

approved