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 A093402 #20 Jul 08 2021 06:20:35
%S A093402 449,44449,444449,444444444444444444444444444444444444444444444449,
%T A093402 444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444449
%N A093402 Primes of the form 40*R_k + 9, where R_k is the repunit (A002275) of length k.
%C A093402 Primes of the form (4*10^k + 41)/9. - _Vincenzo Librandi_, Nov 16 2010
%H A093402 Makoto Kamada, <a href="https://stdkmd.net/nrr/4/44449.htm#prime">Prime numbers of the form 44...449</a>.
%H A093402 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t A093402 Select[Table[FromDigits[PadLeft[{9},n,4]],{n,120}],PrimeQ] (* _Harvey P. Dale_, May 21 2011 *)
%Y A093402 Cf. A056683 (corresponding k).
%K A093402 nonn
%O A093402 1,1
%A A093402 _Rick L. Shepherd_, Mar 28 2004