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Numbers k such that k is a product of two different primes and k-2 is prime.
4

%I #26 Jul 02 2021 01:53:31

%S 15,21,33,39,55,69,85,91,111,115,129,133,141,159,183,201,213,235,253,

%T 259,265,295,309,319,339,355,381,391,403,411,445,451,469,481,489,493,

%U 501,505,511,543,559,565,573,579,589,633,649,655,679,685

%N Numbers k such that k is a product of two different primes and k-2 is prime.

%H Zak Seidov and Michael De Vlieger, <a href="/A043326/b043326.txt">Table of n, a(n) for n = 1..21728</a> (first 10000 terms from Zak Seidov)

%t Select[Range[700],PrimeOmega[#]==PrimeNu[#]==2&&PrimeQ[#-2]&] (* _Harvey P. Dale_, Feb 01 2014 *)

%t Select[Prime[Range[200]]+2,PrimeOmega[#]==PrimeNu[#]==2&] (* _Harvey P. Dale_, Oct 13 2018 *)

%o (PARI) is(n)=isprime(n-2) && bigomega(n)==2 && !issquare(n) \\ _Charles R Greathouse IV_, Jul 20 2014

%Y Cf. A006512, A062721.

%Y Subsequence of A006881.

%K nonn

%O 1,1

%A _Olivier GĂ©rard_, Jul 19 2001