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 A216815 #18 Jun 22 2025 17:35:21
%S A216815 29,41,61,89,101,109,149,181,229,241,269,281,349,389,401,409,421,449,
%T A216815 461,509,521,541,569,601,641,661,701,709,761,769,809,821,829,881,929,
%U A216815 941,1009,1021,1049,1061,1069,1109,1129,1181,1201,1229,1249,1289,1301,1321,1361,1381,1409,1429,1481,1489,1549,1601,1609,1621,1669,1709,1721,1741,1789,1801,1861
%N A216815 Primes congruent to 1 or 9 mod 20.
%C A216815 This is a subsequence of A033205 but it is an important sequence in its own right.
%D A216815 David A. Cox, "Primes of the Form x^2 + n y^2", Wiley, 1989; see p. 33.
%H A216815 Vincenzo Librandi, <a href="/A216815/b216815.txt">Table of n, a(n) for n = 1..1000</a>
%t A216815 Select[Prime[Range[300]], MemberQ[{1, 9}, Mod[#, 20]]&] (* _Vincenzo Librandi_, Mar 22 2013 *)
%o A216815 (Magma) [p: p in PrimesUpTo(2000) | p mod 20 in [1, 9]]; // _Vincenzo Librandi_, Mar 22 2013
%Y A216815 A subsequence of A033205. Cf. A122870.
%K A216815 nonn,easy
%O A216815 1,1
%A A216815 _N. J. A. Sloane_, Sep 20 2012