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 A133127 #22 Jun 07 2024 14:14:42
%S A133127 1,2,4,32,122,388,1580,2302,3436,3866,16993,35263,42601,51251
%N A133127 Numbers k with the property that k followed by k 7's is prime.
%C A133127 The numbers formed by a(1) to a(8) are certified prime and those formed by a(9) and a(10) are prp's.
%C A133127 a(11) > 10000.
%e A133127 2 is a term since 277 is prime.
%t A133127 Select[Range[1600], PrimeQ[#*10^# + 7*(10^# - 1)/9] &] (* _Amiram Eldar_, Jan 27 2021 *)
%o A133127 (PARI) isok(n) = { ss = Str(7*(10^n-1)/9); ispseudoprime(eval(concat(Str(n), ss)));} \\ _Michel Marcus_, Aug 09 2013
%Y A133127 Cf. A084428.
%K A133127 nonn,base,more
%O A133127 1,2
%A A133127 _Ray G. Opao_, Sep 19 2007
%E A133127 a(11) from _Amiram Eldar_, Jan 27 2021
%E A133127 a(12)-a(14) from _Michael S. Branicky_, Jun 06 2024