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 A100473 #21 Jul 08 2021 03:10:04
%S A100473 1,17,23,73,131,473,685,701,1909,3029,3473,4193,9931
%N A100473 Numbers k such that 9*10^k + R_k + 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C A100473 Also numbers k such that (82*10^k + 53)/9 is a prime.
%C A100473 Some of the larger entries may only correspond to probable primes.
%C A100473 a(14) > 10^5. - _Robert Price_, Oct 25 2015
%H A100473 Makoto Kamada, <a href="https://stdkmd.net/nrr/9/91117.htm#prime">Prime numbers of the form 911...117</a>.
%H A100473 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A100473 a(n) = A100999(n) + 1.
%e A100473 n = 1, 17, so that 97 and 911111111111111117 are primes.
%t A100473 Do[ If[ PrimeQ[(82*10^n + 53)/9], Print[n]], {n, 0, 10000}] (* _Robert G. Wilson v_, Jan 19 2005 *)
%Y A100473 Cf. A002275, A100999.
%K A100473 more,nonn
%O A100473 1,2
%A A100473 Julien Peter Benney (jpbenney(AT)ftml.net), Nov 21 2004
%E A100473 a(8)-a(12) from _Robert G. Wilson v_, Jan 12 2005
%E A100473 a(13) from _Robert G. Wilson v_, Jan 12 2005