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 A108327 #25 Jan 17 2019 13:44:08 %S A108327 2,6,32,108,408,1286,2268,2328,4284,53558,181182,249010 %N A108327 Integers n such that 10^n-21 is a prime number. %C A108327 a(13) > 2.5*10^5. - _Robert Price_, Apr 12 2015 %H A108327 Makoto Kamada, <a href="https://stdkmd.net/nrr/aaaba.htm">Near-repdigit numbers of the form AA...AABA</a>. %H A108327 Makoto Kamada, <a href="https://stdkmd.net/nrr/9/99979.htm#prime">Prime numbers of the form 99...9979</a>. %H A108327 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %e A108327 6 is a member because 10^6-21 = 1000000-21 = 999979, which is prime. %Y A108327 Cf. A089675, A095714, A092767. %K A108327 more,nonn %O A108327 1,1 %A A108327 Julien Peter Benney (jpbenney(AT)ftml.net), Jun 30 2005 %E A108327 Edited by _Ray Chandler_, Dec 23 2010 %E A108327 a(10)=53558 from _Robert Price_, Mar 03 2011 %E A108327 a(11)-a(12) from Kamada data by _Robert Price_, Apr 12 2015