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 A099190 #20 Aug 13 2020 14:01:06
%S A099190 1,3,5,6,10,12,13,39,48,54,64,82,147,148,360,399,1638,1876,2146,2194,
%T A099190 15789,23074,38466,68400
%N A099190 Numbers n such that 8*10^n-7 is prime.
%C A099190 Also numbers n such that 7*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C A099190 Primes of the form 7*10^n+9R_n-6 are the only primes which are one more than twice their reversal.
%C A099190 a(25) > 2*10^5. - _Robert Price_, Nov 11 2015
%H A099190 Makoto Kamada, <a href="https://stdkmd.net/nrr/7/79993.htm#prime">Prime numbers of the form 799...993</a>.
%H A099190 Erich Friedman, <a href="https://erich-friedman.github.io/numbers.html">What's Special About This Number?</a>.
%H A099190 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A099190 a(n) = A101155(n) + 1.
%e A099190 73, 7993, 799993, 7999993, etc. are primes.
%t A099190 Do[ If[ PrimeQ[8*10^n - 7], Print[n]], {n, 10000}]
%o A099190 (PARI) is(n)=ispseudoprime(8*10^n-7) \\ _Charles R Greathouse IV_, Feb 20 2017
%Y A099190 Cf. A002275, A099181, A101155.
%K A099190 more,nonn
%O A099190 1,2
%A A099190 _Robert G. Wilson v_, Oct 01 2004
%E A099190 a(19) & a(20) from _Robert G. Wilson v_, Jan 19 2005
%E A099190 a(21)-a(24) from Kamada data by _Robert Price_, Dec 14 2010