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 A124204 #27 Mar 19 2025 10:17:36 %S A124204 2,3,5,9,12,14,20,21,23,26,27,30,32,33,35,38,41,44,47,51,53,59,60,65, %T A124204 66,68,69,74,80,81,86,87,90,93,95,104,107,108,111,114,117,119,122,126, %U A124204 131,137,140,143,150,152,153,156,159,161,165,168,173,177,179,185,188,191 %N A124204 Numbers k such that 20*k + 1 is prime. %H A124204 Harvey P. Dale, <a href="/A124204/b124204.txt">Table of n, a(n) for n = 1..1000</a> %e A124204 If k=95 then 20*k + 1 = 1901 (prime). %t A124204 Select[Range[200],PrimeQ[20#+1]&] (* _Harvey P. Dale_, Mar 19 2025 *) %o A124204 (Magma) [n: n in [0..6000] | IsPrime(20*n + 1)]; // _Vincenzo Librandi_, Mar 26 2010 %o A124204 (PARI) is(n)=isprime(20*n+1) \\ _Charles R Greathouse IV_, Jun 13 2017 %K A124204 nonn,easy %O A124204 1,1 %A A124204 _Parthasarathy Nambi_, Dec 07 2006