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 A270237 #26 Apr 07 2020 22:56:18
%S A270237 131,151,1171,1231,1291,1471,1531,1831,11071,11131,11311,11491,11731,
%T A270237 11971,12391,12511,13171,13591,13831,14011,14431,15031,15091,15991,
%U A270237 16411,16831,17011,17191,17431,17971,18211,19471,19531,110311,110491,111031,111091,111871
%N A270237 Primes which are the decimal concatenation of 1, a prime, and 1.
%C A270237 No padding 0's are allowed: 1021 is not a member even though 02 is prime.
%C A270237 These are the primes that result from A069687.
%C A270237 Subsequence of A208259.
%H A270237 Charles R Greathouse IV, <a href="/A270237/b270237.txt">Table of n, a(n) for n = 1..10000</a>
%e A270237 1171 is a prime which is the concatenation of 1, 17 and 1.
%t A270237 Select[Map[FromDigits@ Flatten@ {1, IntegerDigits@ Prime@ #, 1} &, Range@ 200], PrimeQ] (* _Michael De Vlieger_, Mar 15 2016 *)
%t A270237 Select[FromDigits[Flatten[IntegerDigits/@Join[{1},#,{1}]]]&/@Prime[ Range[ 200]], PrimeQ] (* _Harvey P. Dale_, Jul 26 2016 *)
%o A270237 (PARI) lista(nn) = forprime(p=2, nn, if(isprime(P=eval(Str(1, p, 1))), print1(P, ", "))); \\ _Altug Alkan_, Mar 13 2016
%o A270237 (PARI) is(n)=my(d=digits(n)); isprime(n) && d[1]==1 && #d>2 && d[2] && d[#d]==1 && isprime(fromdigits(d[2..#d-1])) \\ _Charles R Greathouse IV_, Mar 15 2016
%Y A270237 Cf. A000040, A069687, A208259.
%K A270237 nonn,base
%O A270237 1,1
%A A270237 _Emre APARI_, Mar 13 2016