A192321 - OEIS

%I #30 Jun 13 2017 16:39:04

%S 6,14,15,21,33,38,57,62,69,77,111,119,141,143,155,161,194,203,206,209,

%T 215,218,278,287,309,314,329,381,395,398,447,453,489,533,537,551,554,

%U 566,579,626,635,671,755,785,818,878,899,959,974,993,1007,1011,1041,1067,1077,1133,1142,1149,1191,1202,1263

%N Semiprime numbers n such that n^2 + n + 1 is prime.

%H Harvey P. Dale, <a href="/A192321/b192321.txt">Table of n, a(n) for n = 1..1000</a>

%e 309 is in the sequence because 309 is semiprime (309 = 3 * 103) and 309^2 + 309 + 1 = 95791 is prime.

%t Select[Range[2000],PrimeOmega[#]==2&&PrimeQ[#^2+#+1]&] (* _Harvey P. Dale_, Feb 26 2013 *)

%o (PARI) issemi(n)=bigomega(n)==2

%o is(n)=isprime(n^2+n+1) && issemi(n) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Intersection of A182253 and A001358.

%Y Subsequence of A182253.

%K nonn,easy

%O 1,1

%A _Jonathan Vos Post_, Dec 19 2012