%I A104873
%S A104873 611000000000061,1631000000000163,1931000000000193,2111000000000211,
%T A104873 2711000000000271,3311000000000331,5471000000000547,6611000000000661,
%U A104873 7511000000000751,7871000000000787,9971000000000997,10511000000001051
%N A104873 Concatenations of pairs of primes that differ by 10^12.
%C A104873 Integers in this sequence can never be prime, as they are all multiples 
               of 3. They can be semiprimes, as is the case for Prime(177) concatenated 
               with Prime(37607912056) = 10511000000001051 = 3 * 3503666666667017.
%F A104873 a(n) = Concatenate(P, P+10^12) iff P prime and P+10^12 prime.
%e A104873 61 is prime, specifically prime(18) and 61 + 10^12 is prime, specifically 
               prime(7607912020), so their concatenation is in this sequence: 611000000000061. 
               The concatenation is not itself prime, as it equals 3 * 7 * 23 * 
               1265010351967.
%Y A104873 Cf. A000040, A001358, A023201, A100750, A103195, A103206, A104718, A104719, 
               A103523, A103534, A103576, A103617.
%Y A104873 Sequence in context: A011528 A128769 A086438 this_sequence A088867 A159042 
               A129935
%Y A104873 Adjacent sequences: A104870 A104871 A104872 this_sequence A104874 A104875 
               A104876
%K A104873 base,easy,nonn
%O A104873 1,1
%A A104873 Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 29 2005