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A383468 Semiprimes s = A001358(k) such that k, s - k and s + k are also semiprimes.

%I A383468 #7 Apr 29 2025 13:27:59
%S A383468 10,15,141,166,274,298,299,687,995,1115,1227,1299,1345,1891,1945,2194,
%T A383468 2661,2998,3093,3287,3566,3781,3902,4174,4262,4497,4798,5378,5414,
%U A383468 5758,6609,7094,7666,8354,8434,9566,10041,10342,11051,11091,11486,11582,11702,12279,12574,13154,13346,13387,13466
%N A383468 Semiprimes s = A001358(k) such that k, s - k and s + k are also semiprimes.
%C A383468 Except for a(1) = 10 = A001358(4), s and k always have different parities.
%H A383468 Robert Israel, <a href="/A383468/b383468.txt">Table of n, a(n) for n = 1..10000</a>
%F A383468 a(n) = A001358(A383469(n)).
%e A383468 a(3) = 141 is a term because 141 = 3 * 47 = A001358(46) is a semiprime and 46 = 2 * 23, 141 - 46 = 95 = 5 * 19 and 141 + 46 = 187 = 11 * 17 are all semiprimes.
%p A383468 k:= 0: R:= NULL: count:= 0:
%p A383468 for s from 1 while count < 100 do
%p A383468   if numtheory:-bigomega(s) = 2 then
%p A383468     k:= k+1;
%p A383468     if andmap(t -> numtheory:-bigomega(t) = 2, [k, s-k, s+k]) then
%p A383468       R:= R, s; count:= count+1;
%p A383468     fi
%p A383468   fi;
%p A383468 od:
%p A383468 R;
%Y A383468 Cf. A001358. A383469.
%K A383468 nonn
%O A383468 1,1
%A A383468 _Zak Seidov_ and _Robert Israel_, Apr 27 2025