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A034815 Concatenations C1 and C2 are both prime (see the comment lines). 0

%I #11 Jul 16 2022 07:10:25

%S 33,51,53,63,111,123,129,211,237,273,357,489,519,573,597,609,639,651,

%T 653,657,669,681,687,747,753,819,831,873,891,987,997,1071,1611,1881,

%U 2037,2049,2247,2271,2613,2763,3063,3267,3393,3573,3969,4251,4263,4293

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

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

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

%e n=1881 -> next prime is 1889, previous prime is 1879, thus '18891881' and '18811879' are both primes.

%t okQ[n_]:=Module[{idn=IntegerDigits[n],ida,idb},ida=IntegerDigits[NextPrime[n,-1]];idb=IntegerDigits[NextPrime[n]];PrimeQ[FromDigits[Join[idn,ida]]]&&PrimeQ[FromDigits[Join[idb,idn]]]]

%t Select[Range[5000],okQ] (* _Harvey P. Dale_, Dec 25 2010 *)

%Y Cf. A034808-A034821.

%K nonn,base

%O 0,1

%A _Patrick De Geest_, Oct 15 1998

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)