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%I #9 Mar 30 2018 11:57:19
%S 511,713,1117,1319,1723,2329,3137,3743,4147,4753,5359,6167,6773,7379,
%T 8389,97103,101107,103109,107113,131137,151157,157163,167173,173179,
%U 191197,193199,223229
%N Concatenations of pairs of primes that differ by 6.
%C Prime in this sequence: a(3) = 1117, a(4) = 1319, a(5) = 1723, a(7) = 3137, a(15) = 8389, a(16) = 97103, a(17) = 101107, a(21) = 151157, a(22) = 157163, a(23) = 167173, a(27) = 223229. Semiprimes in this sequence: a(1) = 511 = 7 x 73, a(2) = 713 = 23 * 31, a(6) = 2329 = 17 * 137, a(8) = 3743 = 19 * 197, a(11) = 5359 = 23 * 233, a(12) = 6167 = 7 * 881, a(13) = 6773 = 13 * 521, a(14) = 7379 = 47 x 157, a(18) = 103109 = 23 * 4483, a(20) = 131137 = 71 * 1847, a(26) = 193199 = 43 * 4493, ... Note that a(9) = 4147 = 11 * 13 * 29 and a(19) = 107113 = 43 * 47 * 53 are the products of three primes with the same number of digits.
%H Harvey P. Dale, <a href="/A103206/b103206.txt">Table of n, a(n) for n = 0..1000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/SexyPrimes.html">Sexy Primes.</a>
%H T. Trotter, <a href="http://www.trottermath.net/numthry/sexyprim.html">"Sexy Primes."</a> [Warning: As of March 2018 this site appears to have been hacked. Proceed with great caution. The original content should be retrieved from the Wayback machine and added here. - _N. J. A. Sloane_, Mar 29 2018]
%F a(n) = A023201(n) concatenated with A023201(n)+6.
%t FromDigits[Flatten[IntegerDigits/@{#,#+6}]]&/@Select[Prime[Range[50]], PrimeQ[#+6]&] (* _Harvey P. Dale_, Jun 24 2015 *)
%Y Cf. A023201, A046117.
%Y Cf. A000040, A103195.
%K base,easy,nonn
%O 0,1
%A _Jonathan Vos Post_, Mar 19 2005
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