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 A268859 #37 Sep 08 2022 08:46:15
%S A268859 421,521,821,1021,1321,1621,1721,2221,2521,2621,3121,3221,3821,4021,
%T A268859 4421,4621,4721,5021,5521,5821,6121,6221,6421,6521,7121,7321,7621,
%U A268859 8221,8521,8821,9221,9421,9521,9721,10321,11321,11621,11821,12421,12721,12821,13121
%N A268859 Prime numbers ending in 21.
%p A268859 A268859:=n->`if`(isprime(n) and n mod 100 = 21, n, NULL): seq(A268859(n), n=1..5*10^4); # _Wesley Ivan Hurt_, Apr 02 2016
%t A268859 Select[Table[21 + 100 i, {i, 0, 10^3}], ProvablePrimeQ[#] &]
%o A268859 (Magma) [n: n in PrimesUpTo(15000) | n mod 100 eq 21]; // _Vincenzo Librandi_, Feb 15 2016
%o A268859 (PARI) lista(nn) = {for(n=1, nn, if (isprime(p=100*n+21), print1(p, ", ")););} \\ _Michel Marcus_, Feb 20 2016
%o A268859 (Python)
%o A268859 from sympy import isprime
%o A268859 for n in range(421,15000,100):
%o A268859 if(isprime(n)):print(n)
%o A268859 # _Soumil Mandal_, Apr 03 2016
%Y A268859 Cf. A268858, A268860.
%K A268859 nonn,base
%O A268859 1,1
%A A268859 _Soumadeep Ghosh_, Feb 14 2016