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 A240843 #8 Apr 16 2014 05:39:47
%S A240843 773,1103,1301,3947,3989,4241,4637,4931,5039,5387,5417,6803,6917,6971,
%T A240843 7229,7451,7703,7753,10211,10303,10337,10607,10657,10723,10859,11117,
%U A240843 11399,11423,11489,11717,11813,11971,11987,12119,12329,12541,12653,12659,12907,12983
%N A240843 Primes p with property that appending or prepending any single decimal digit to p does not produce a prime.
%F A240843 A119289 INTERSECT A155762.
%e A240843 1103 belongs to this sequence because 10*1103 + k and k*10^4 + 1103, for k = 1 to 9, are all composite.
%t A240843 fQ[n_] := Block[{e = Floor[ Log10@ n] + 1, r = Range@ 9}, Union@ Flatten[ PrimeQ[{10 n + r, r*10^e + n}]] == {False}]; Select[ Prime@ Range@ 1550, fQ] (* _Robert G. Wilson v_, Apr 15 2014 *)
%o A240843 (PARI) for(n=2, 12983, v=n; if(isprime(n), s=#Str(v); t=0; for(k=1, 9, if(isprime(10*v+k)||isprime(k*10^s+v), break, t++)); if(t==9, print1(v, ", "))); n=v);
%Y A240843 Subsequence of A119289 and of A155762.
%K A240843 nonn,base
%O A240843 1,1
%A A240843 _Arkadiusz Wesolowski_, Apr 13 2014