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 A099017 #27 Jul 08 2021 03:14:54
%S A099017 0,1,2,6,10,12,13,22,32,46,61,68,90,110,652,1608,1904,2003,3038,3086,
%T A099017 9580,9698,10639,14461
%N A099017 Numbers k such that 4*10^k + 6*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
%C A099017 Also numbers k such that (14*10^k + 1)/3 is prime.
%C A099017 a(25) > 2*10^5. - _Robert Price_, Jul 11 2015
%H A099017 Makoto Kamada, <a href="https://stdkmd.net/nrr/4/46667.htm#prime">Prime numbers of the form 466...667</a>.
%H A099017 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A099017 a(n) = A101731(n-1) + 1, for n>1.
%e A099017 n = 1, 2, 6 are members since 47, 467, 4666667 are primes.
%t A099017 Do[ If[ PrimeQ[(14*10^n + 1)/3], Print[n]], {n, 0, 10000}] (* _Robert G. Wilson v_, Jan 17 2005 *)
%Y A099017 Cf. A002275, A099005, A098959, A101731.
%K A099017 more,nonn
%O A099017 1,3
%A A099017 Julien Peter Benney (jpbenney(AT)ftml.net), Nov 13 2004
%E A099017 a(15)-a(22) from _Robert G. Wilson v_, Jan 17 2005
%E A099017 a(23)-a(24) from Kamada data by _Robert Price_, Dec 08 2010
%E A099017 Prepended a(1)=0 by _Robert Price_, Jul 11 2015