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 A178434 #23 Jan 17 2019 13:44:08
%S A178434 2,3,4,5,7,9,10,14,22,98,127,151,158,274,377,1015,2146,8499,13885,
%T A178434 13991,17834,18211,36271,52317,53804,104212,117059,178695
%N A178434 Numbers n such that 10^n - 71 is prime.
%C A178434 a(29) > 2.5*10^5. - _Robert Price_, Apr 12 2015
%H A178434 Makoto Kamada, <a href="https://stdkmd.net/nrr/aaaba.htm">Near-repdigit numbers of the form AA...AABA</a>.
%H A178434 Makoto Kamada, <a href="https://stdkmd.net/nrr/9/99929.htm#prime">Prime numbers of the form 99...9929</a>.
%H A178434 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%e A178434 10^4 - 71 = 9929 which is a prime number.
%t A178434 nMax=1000; Do[If[PrimeQ[10^n-71], Print[n]], {n, nMax}]
%o A178434 (PARI) is(n)=ispseudoprime(10^n-71) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A178434 Cf. A108330, A108328.
%K A178434 more,nonn
%O A178434 1,1
%A A178434 _Robert Price_, Dec 21 2010
%E A178434 a(24:25)=52317,53804 from _Robert Price_, Apr 25 2011
%E A178434 a(26)-a(28) from Kamada data by _Robert Price_, Apr 12 2015