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A296020 Number of primes of the form 4*k+3 <= 4*n+3.

%I A296020 #15 Aug 10 2019 13:24:21
%S A296020 1,2,3,3,4,5,5,6,6,6,7,8,8,8,9,9,10,11,11,12,13,13,13,13,13,14,15,15,
%T A296020 15,15,15,16,17,17,18,18,18,19,19,19,20,21,21,21,22,22,22,23,23,24,24,
%U A296020 24,25,25,25,26,27,27,27,28,28,28,29,29,29,30,30,31,31,31
%N A296020 Number of primes of the form 4*k+3 <= 4*n+3.
%H A296020 Seiichi Manyama, <a href="/A296020/b296020.txt">Table of n, a(n) for n = 0..10000</a>
%t A296020 Module[{nn=300,pr3},pr3=Table[If[PrimeQ[k]&&Mod[k,4]==3,1,0],{k,0,nn}];Table[Total[Take[pr3,4n+3]],{n,(nn-3)/4}]] (* _Harvey P. Dale_, Aug 10 2019 *)
%o A296020 (Ruby)
%o A296020 require 'prime'
%o A296020 def A(k, n)
%o A296020   ary = []
%o A296020   cnt = 0
%o A296020   k.step(4 * n + k, 4){|i|
%o A296020     cnt += 1 if i.prime?
%o A296020     ary << cnt
%o A296020   }
%o A296020   ary
%o A296020 end
%o A296020 p A(3, 100)
%Y A296020 Cf. A004767, A091099, A295996, A296021.
%K A296020 nonn
%O A296020 0,2
%A A296020 _Seiichi Manyama_, Dec 02 2017