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 A111021 #28 Sep 08 2022 08:45:20 %S A111021 1,8,11,143,203,2727,2911,3339,17039 %N A111021 Integers k such that 7*10^k + 31 is a prime number. %C A111021 See Kamada link - primecount.txt for terms, primesize.txt for discovery details including probable or proved primes - search on "70031". %C A111021 a(10) > 10^5. - _Robert Price_, Jan 28 2017 %H A111021 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/">List of near-repdigit-related prime numbers</a>. %H A111021 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %e A111021 k = 11 is a term because 7*10^11 + 31 = 7*100000000000 + 31 = 700000000000 + 31 = 700000000031, which is a prime. %t A111021 Select[Range[0, 10000], PrimeQ[7 10^# + 31] &] (* _Vincenzo Librandi_, Jul 03 2016 *) %o A111021 (Magma) [n: n in [1..300] | IsPrime(7*10^n+31)]; // _Vincenzo Librandi_, Jul 03 2016 %Y A111021 Cf. A049054, A088274, A088275, A095688, A107083, A108049, A108050, A108052, A108054, A110980. %K A111021 nonn,more %O A111021 1,2 %A A111021 Julien Peter Benney (jpbenney(AT)ftml.net), Oct 04 2005 %E A111021 a(9) from _Ray Chandler_, Dec 23 2010 %E A111021 a(1) = 1 prepended by _Vincenzo Librandi_, Jul 03 2016