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 A268448 #27 May 31 2024 22:11:33
%S A268448 1,2,4,5,6,7,14,21,27,34,53,72,96,145,168,191,192,309,393,502,667,
%T A268448 1055,1534,1710,4171,4838,4950,9932,10860,11906,14148,17184,27054,
%U A268448 31435
%N A268448 Numbers k such that (35*10^k - 11)/3 is prime.
%C A268448 Numbers k such that digits 11 followed by k-1 occurrences of digit 6 followed by digit 3 is prime. E.g., 116666...666663.
%C A268448 a(35) > 3*10^5. - _Robert Price_, Oct 16 2015
%H A268448 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 116w3</a>.
%e A268448 7 is in this sequence because (35*10^7 - 11)/3 = 116666663 is prime.
%t A268448 Select[Range[0, 100000], PrimeQ[(35*10^# - 11)/3] &]
%o A268448 (Magma) [n: n in [0..400] |IsPrime((35*10^n-11) div 3)]; // _Vincenzo Librandi_, Feb 05 2016
%o A268448 (PARI) lista(nn) = {for(n=1, nn, if(ispseudoprime((35*10^n-11)/3), print1(n, ", ")));} \\ _Altug Alkan_, Feb 05 2016
%Y A268448 Cf. A056654.
%K A268448 more,nonn
%O A268448 1,2
%A A268448 _Robert Price_, Feb 04 2016