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 A145851 #12 Jun 22 2022 15:42:33
%S A145851 19,49999,599999,1799999999999999999,2099999999999999999999,
%T A145851 289999999999999999999999999999
%N A145851 Primes of the form k followed by k 9's.
%C A145851 Corresponding k, which cannot be multiples of 3, are in A174352. The next term has 176 digits, too large to include here. - _Rick L. Shepherd_, Mar 22 2010
%t A145851 Select[Table[FromDigits[PadRight[{k},k+1,9]],{k,200}],PrimeQ] (* _Harvey P. Dale_, Jun 22 2022 *)
%o A145851 (PARI) lista(nn) = for(k=1, nn, if(ispseudoprime(q=k*10^(k-1)-1), print1(q, ", "))); \\ _Jinyuan Wang_, Mar 24 2020
%Y A145851 Cf. A141311, A145852.
%Y A145851 Cf. A174352. - _Rick L. Shepherd_, Mar 22 2010
%K A145851 nonn,base
%O A145851 1,1
%A A145851 _Lekraj Beedassy_, Oct 21 2008
%E A145851 a(2) was 4999; corrected by _Rick L. Shepherd_, Mar 22 2010