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 A178406 #24 Jan 17 2019 13:44:08 %S A178406 2,6,8,12,14,47,88,130,414,1388,1932,4106,4412,12870,22956,23932, %T A178406 27312,35316,37169,43873,150029 %N A178406 Numbers n such that 10^n - 41 is prime. %C A178406 The next term, if one exists, is >100000. - _Robert Price_, Apr 25 2011 %C A178406 a(22) > 2.5*10^5. - _Robert Price_, Apr 12 2015 %H A178406 Makoto Kamada, <a href="https://stdkmd.net/nrr/aaaba.htm">Near-repdigit numbers of the form AA...AABA</a>. %H A178406 Makoto Kamada, <a href="https://stdkmd.net/nrr/9/99959.htm#prime">Prime numbers of the form 99...9959</a>. %H A178406 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %e A178406 10^6 - 41 = 999959 which is a prime number. %t A178406 m=1000; For[n=1, n<m, If[PrimeQ[10^n-41], Print[n]]; n++ ] %o A178406 (PARI) is(n)=ispseudoprime(10^n-41) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A178406 Cf. A108330, A108328. %K A178406 more,nonn %O A178406 1,1 %A A178406 _Robert Price_, Dec 21 2010 %E A178406 a(20)=43873 from _Robert Price_, Apr 25 2011 %E A178406 a(21) from Kamada data by _Robert Price_, Apr 12 2015