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 A124826 #14 Sep 08 2022 08:45:28 %S A124826 43,127,211,337,379,421,463,547,631,673,757,883,967,1009,1051,1093, %T A124826 1303,1429,1471,1597,1723,1933,2017,2143,2269,2311,2437,2521,2647, %U A124826 2689,2731,2857,3067,3109,3319,3361,3529,3571,3613,3697,3739,3823,3907,4159,4201 %N A124826 Primes congruent to 1 mod 21. %H A124826 Vincenzo Librandi, <a href="/A124826/b124826.txt">Table of n, a(n) for n = 1..1000</a> %t A124826 Select[Range[1,5000,21],PrimeQ] (* _Vladimir Joseph Stephan Orlovsky_, Apr 03 2011*) %o A124826 (Magma) [p: p in PrimesUpTo(5000) | p mod 21 eq 1 ]; // _Vincenzo Librandi_, Aug 14 2012 %o A124826 (PARI) is(n)=isprime(n) && n%21==1 \\ _Charles R Greathouse IV_, Jul 01 2016 %Y A124826 Cf. A000040, A141881. %K A124826 nonn,easy %O A124826 1,1 %A A124826 _N. J. A. Sloane_, Jul 11 2008