A113527 - OEIS

%I #15 Oct 09 2022 05:20:43

%S 15,115,155,201,253,445,785,1345,2215,3503,3711,4145,4841,5853,6395,

%T 7855,9131,12353,13535,14353,16503,18331,19281,20255,20751,21253,

%U 21761,23853,24935,26603,29503,30101

%N Semiprimes in A056108.

%C Intersection of A056108 and A001358.

%H Michael De Vlieger, <a href="/A113527/b113527.txt">Table of n, a(n) for n = 1..10000</a>

%F {a(n)} = {3*n^2 + n + 1 iff semiprime}. {a(n)} = A056108 INTERSECT A001358.

%e a(1) = 15 because A056108(2) = 15 = 3 * 5 is semiprime.

%e a(2) = 115 because A056108(6) = 115 = 5 * 23 is semiprime.

%e a(32) = 30101 because A056108(100) = 30101 = 31 * 971 is semiprime.

%t Select[Array[3 #^2 + # + 1 &, 100], PrimeOmega[#] == 2 &] (* _Michael De Vlieger_, Mar 17 2021 *)

%Y Cf. A001358, A056108.

%Y Cf. A113519, A113524, A113525, A113528, A113530.

%K easy,nonn

%O 1,1

%A _Jonathan Vos Post_, Jan 12 2006