This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A034818 #8 Oct 06 2019 18:17:54
%S A034818 657,4929,10647,18291,20907,22653,27381,28053,28671,42471,48441,57363,
%T A034818 69651,79569,89853,93261,95967,101283,110763,119481,128613,145719,
%U A034818 149409,174993,201417,204861,205329,221883,248391,269199,272799,293451
%N A034818 Concatenations C1 and C2 and C3 are all prime (see the comment lines).
%C A034818 C1 = 'nextprime(n) followed by n'
%C A034818 C2 = 'n followed by prevprime(n)'
%C A034818 C3 = 'nextprime(n) followed by n followed by prevprime(n)'
%e A034818 n=95967 -> next prime is 95971, previous prime is 95959, thus '9597195967' and '9596795959' and '959719596795959' are all three primes.
%t A034818 ccatQ[n_]:=Module[{idn=IntegerDigits[n],pp=IntegerDigits[NextPrime[n,-1]], np= IntegerDigits[ NextPrime[n]]}, And@@PrimeQ[{FromDigits[ Join[np, idn]], FromDigits[Join[idn,pp]],FromDigits[Join[np,idn,pp]]}]]; Select[ Range[300000],ccatQ] (* _Harvey P. Dale_, Sep 09 2011 *)
%Y A034818 Cf. A034808-A034821.
%K A034818 nonn,base
%O A034818 0,1
%A A034818 _Patrick De Geest_, Oct 15 1998