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 A121326 #23 Feb 12 2023 20:22:22
%S A121326 5,17,37,101,197,257,401,577,677,1297,1601,2917,3137,4357,5477,7057,
%T A121326 8101,8837,12101,13457,14401,15377,15877,16901,17957,21317,22501,
%U A121326 24337,25601,28901,30977,32401,33857,41617,42437,44101,50177,52901,55697
%N A121326 Primes of the form 4*k^2 + 1.
%C A121326 Except for the initial 2 in A002496 this sequence is the same as A002496.
%C A121326 The prime factors of numbers of the form 4k^2 + 1 (a sum of two squares) are of the form 4m + 1.
%H A121326 Vincenzo Librandi, <a href="/A121326/b121326.txt">Table of n, a(n) for n = 1..10000</a>
%e A121326 For k=4, 4k^2 + 1 = 17, a prime.
%t A121326 Select[Table[4n^2+1,{n,0,800}],PrimeQ] (* _Vincenzo Librandi_, Dec 02 2011 *)
%o A121326 (PARI) for(x=1,200,y=4*x^2+1;if(isprime(y),print1(y",")))
%o A121326 (Magma) [a: n in [0..400] | IsPrime(a) where a is 4*n^2+1]; // _Vincenzo Librandi_, Dec 02 2011
%Y A121326 Cf. A002496.
%K A121326 nonn,easy
%O A121326 1,1
%A A121326 _Cino Hilliard_, Aug 26 2006