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 A139513 #27 Dec 15 2024 12:48:06
%S A139513 3,7,23,29,41,43,47,61,67,83,89,101,103,107,109,127,149,163,167,181,
%T A139513 223,227,229,241,263,269,281,283,307,347,349,367,383,389,401,409,421,
%U A139513 443,449,461,463,467,487,503,509,521,523,541,547,563,569,587,601,607,641
%N A139513 Primes congruent to {1, 3, 7, 9} mod 20.
%C A139513 Rational primes that decompose in the field Q(sqrt(-5)). - _N. J. A. Sloane_, Dec 25 2017
%D A139513 Dirichlet & Dedekind, Lectures on Number Theory (English Translation 1999), p. 119.
%D A139513 David A. Cox, Primes of the Form x^2 + n y^2, Wiley, 1989, p. 14 (1.8), p. 32 (2.19).
%H A139513 Vincenzo Librandi, <a href="/A139513/b139513.txt">Table of n, a(n) for n = 1..1000</a>
%H A139513 <a href="https://oeis.org/index/Pri#primes_decomp_of">Index to sequences related to decomposition of primes in quadratic fields</a>
%F A139513 a(n) ~ 2n log n. - _Charles R Greathouse IV_, Nov 29 2016
%F A139513 Legendre symbol (-5, a(n)) = +1. One sets (-5, 5) = 0 and for odd primes p == -1, -3, -7, -9 (mod 20) (-5, p) = -1, given in A003626. - _Wolfdieter Lang_, Mar 05 2021
%t A139513 a = {}; Do[If[MemberQ[{1, 3, 7, 9}, Mod[Prime[n], 20]], AppendTo[a, Prime[n]]], {n, 1, 200}]; a (*Artur Jasinski*)
%t A139513 Select[Prime[Range[200]],MemberQ[{1,3,7,9},Mod[#,20]]&] (* _Vincenzo Librandi_, Aug 15 2012 *)
%o A139513 (Magma) [ p: p in PrimesUpTo(700) | p mod 20 in [1,3,7,9] ]; // _Vincenzo Librandi_, Aug 15 2012
%o A139513 (PARI) select(p->my(k=p%20); k==1 || k==3 || k==7 || k==9, primes(100)) \\ _Charles R Greathouse IV_, Nov 29 2016
%Y A139513 Cf. A296922, A003626.
%K A139513 nonn,easy
%O A139513 1,1
%A A139513 _Artur Jasinski_, Apr 25 2008