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A034820 Concatenations C1 and C2 and C3 and C4 are all prime (see the comment lines). 1

%I

%S 16776,41719,164612,188435,188682,312184,317594,392771,397617,450413,

%T 476055,486283,492240,497913,539471,584029,620029,640883,648445,

%U 656757,903009,992790,993475,995917,1045387,1082078,1194606,1252496,1322841

%N Concatenations C1 and C2 and C3 and C4 are all prime (see the comment lines).

%C C1 = 'prevprime(n) followed by n followed by prevprime(n)'

%C C2 = 'prevprime(n) followed by n followed by nextprime(n)'

%C C3 = 'nextprime(n) followed by n followed by prevprime(n)'

%C C4 = 'nextprime(n) followed by n followed by nextprime(n)'

%e n=41719 -> next prime is 41729, previous prime is 41687, thus '416874171941687' and '416874171941729' and '417294171941687' and '417294171941729' are all four primes.

%Y Cf. A034808-A034821.

%K nonn,base

%O 0,1

%A _Patrick De Geest_, Oct 15 1998

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Last modified February 8 11:17 EST 2023. Contains 360138 sequences. (Running on oeis4.)