A276626 - OEIS

%I #10 Sep 07 2016 12:03:55

%S 10,22,34,58,94,142,178,202,214,382,394,454,502,538,634,718,922,934,

%T 1042,1138,1294,1318,1402,1438,1642,1714,1762,1822,1858,1894,1942,

%U 2182,2218,2362,2434,2518,2578,2722,2734,2902,2974,3118,3274,3694,3778,3958,4198,4282,4414,4534,4594,4678

%N Semiprimes n such that (n-1)/3 is prime.

%C All semiprimes in A175666 are terms: a(2)=10=A175666(2), a(3)=34=A175666(4),etc.

%H Charles R Greathouse IV, <a href="/A276626/b276626.txt">Table of n, a(n) for n = 1..10000</a>

%e 10=2*5 and (10-1)/3=3 prime, 22=2*11 and (22-1)/3=7 prime.

%t Reap[Do[If[PrimeQ[(a=1+3*Prime[k])/2],Sow[a]],{k,1000}]][[2,1]]

%o (PARI) isok(n) = (bigomega(n)==2) && (((n-1) % 3)==0) && isprime((n-1)/3); \\ _Michel Marcus_, Sep 07 2016

%o (PARI) is(n)=n%3==1 && isprime(n\3) && bigomega(n)==2 \\ _Charles R Greathouse IV_, Sep 07 2016

%Y Cf. A175666.

%K nonn

%O 1,1

%A _Zak Seidov_, Sep 07 2016