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 A096508 #32 Apr 30 2024 06:06:02
%S A096508 2,14,17,35,4175,4472,9812,12260,12341,13760,14576,53411,144683,148328
%N A096508 Numbers k for which 8*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C A096508 Also numbers k such that (8*10^k + 1)/9 is prime.
%C A096508 a(15) > 2*10^5. - _Robert Price_, Sep 06 2014
%H A096508 Makoto Kamada, <a href="https://stdkmd.net/nrr/8/88889.htm#prime">Prime numbers of the form 88...889</a>.
%H A096508 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%F A096508 a(n) = A056663(n) + 1.
%e A096508 35 is a term because 88888888888888888888888888888888889 (34 8's) is a prime number.
%p A096508 select(n -> isprime((8*10^n+1)/9), [$1..10000]); # _Robert Israel_, Sep 07 2014
%t A096508 Do[ If[ PrimeQ[ 8(10^n - 1)/9 + 1], Print[n]], {n, 0, 30000}] (* _Robert G. Wilson v_, Oct 15 2004 *)
%o A096508 (PARI)
%o A096508 for(n=1,10^4,if(ispseudoprime(8*(10^n-1)/9+1),print1(n,", "))) \\ _Derek Orr_, Sep 06 2014
%Y A096508 Cf. A002275, A056663, A096503-A096507.
%K A096508 nonn
%O A096508 1,1
%A A096508 _Labos Elemer_, Jul 12 2004
%E A096508 Four missing terms (9812, 12260, 12341, 13760) added, and a(12)-a(14) added from Kamada data, by _Robert Price_, Sep 06 2014