%I A034820
%S A034820 16776,41719,164612,188435,188682,312184,317594,392771,397617,450413,
%T A034820 476055,486283,492240,497913,539471,584029,620029,640883,648445,656757,
%U A034820 903009,992790,993475,995917,1045387,1082078,1194606,1252496,1322841
%N A034820 Concatenations C1 and C2 and C3 and C4 are all prime (see the comment 
               lines).
%C A034820 C1 = 'prevprime(n) followed by n followed by prevprime(n)'
%C A034820 C2 = 'prevprime(n) followed by n followed by nextprime(n)'
%C A034820 C3 = 'nextprime(n) followed by n followed by prevprime(n)'
%C A034820 C4 = 'nextprime(n) followed by n followed by nextprime(n)'
%e A034820 n=41719 -> next prime is 41729, previous prime is 41687, thus '416874171941687' 
               and '416874171941729' and '417294171941687' and '417294171941729' 
               are all four primes.
%Y A034820 Cf. A034808-A034821.
%Y A034820 Sequence in context: A128383 A052190 A068784 this_sequence A053074 A115923 
               A147698
%Y A034820 Adjacent sequences: A034817 A034818 A034819 this_sequence A034821 A034822 
               A034823
%K A034820 nonn,base
%O A034820 0,1
%A A034820 Patrick De Geest (pdg(AT)worldofnumbers.com), Oct 15 1998.