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A112776 Numbers n such that 6n+5 is semiprime. 2

%I

%S 5,10,12,15,19,23,25,26,30,33,34,35,36,47,49,50,53,54,55,56,60,61,62,

%T 65,67,68,72,78,80,82,85,87,88,90,91,96,101,103,104,105,111,114,115,

%U 117,118,121,122,124,125,127,129,130,131,133,135,141,144,148,149,150

%N Numbers n such that 6n+5 is semiprime.

%C Resulting semiprimes in A108172.

%H Vincenzo Librandi, <a href="/A112776/b112776.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = (A108172(n) - 5)/6.

%t Select[Range[3000], Plus@@Last/@FactorInteger[6# + 5] == 2&] (* _Vincenzo Librandi_, Sep 22 2012 *)

%o (MAGMA) IsSemiprime:=func<n | &+[k[2]: k in Factorization(n)] eq 2>; [n: n in [2..150] | IsSemiprime(6*n+5)]; // _Vincenzo Librandi_, Sep 22 2012

%o (PARI) is(n)=bigomega(6*n+5)==2 \\ _Charles R Greathouse IV_, Feb 08 2017

%K easy,nonn

%O 1,1

%A _Jonathan Vos Post_ and _Ray Chandler_, Oct 15 2005

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Last modified January 19 21:47 EST 2020. Contains 331066 sequences. (Running on oeis4.)