%I #9 Aug 13 2024 22:53:48

%S 9,51,63,87,111,123,153,177,207,211,239,263,273,289,327,333,343,359,

%T 407,471,489,497,513,541,597,621,651,659,663,681,687,693,697,747,753,

%U 793,819,831,869,909,977,987,1027,1041,1089,1131,1143,1239,1491,1611

%N Concatenations C1 and C2 are both prime (see the comment lines).

%C C1 = 'prevprime(k) followed by k'.

%C C2 = 'k followed by prevprime(k)'.

%H Andrew Howroyd, <a href="/A034814/b034814.txt">Table of n, a(n) for n = 1..1000</a>

%e n=747 -> previous prime is 743, thus '743747' and '747743' are both primes.

%Y Intersection of A034808 and A034809.

%Y Cf. A034810-A034821.

%K nonn,base

%O 1,1

%A _Patrick De Geest_, Oct 15 1998

%E Offset changed by _Andrew Howroyd_, Aug 13 2024