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 A066490 #16 Oct 22 2021 12:40:04
%S A066490 0,0,1,1,1,1,2,2,2,2,3,3,3,3,3,3,3,3,4,4,4,4,5,5,5,5,5,5,5,5,6,6,6,6,
%T A066490 6,6,6,6,6,6,6,6,7,7,7,7,8,8,8,8,8,8,8,8,8,8,8,8,9,9,9,9,9,9,9,9,10,
%U A066490 10,10,10,11,11,11,11,11,11,11,11,12,12,12,12,13,13,13,13,13,13,13,13,13
%N A066490 Number of primes of the form 4m+3 that are <= n.
%C A066490 Partial sums of A079261. - _Reinhard Zumkeller_, Feb 06 2014
%H A066490 T. D. Noe, <a href="/A066490/b066490.txt">Table of n, a(n) for n=1..10000</a>
%F A066490 A066339(n) + a(n) = A000720(n) - 1 for n >= 2. - _Jianing Song_, Apr 28 2021
%t A066490 Table[ Length[ Select[ Union[ Table[ Prime[ PrimePi[i]], {i, 2, n}]], Mod[ #, 4] == 3 & ]], {n, 2, 100} ]
%t A066490 Accumulate[Table[If[PrimeQ[n]&&Mod[n,4]==3,1,0],{n,100}]] (* _Harvey P. Dale_, Mar 17 2021 *)
%o A066490 (PARI) for(n=1,100,print1(sum(i=1,n,if((i*isprime(i)-3)%4,0,1)),","))
%o A066490 (Haskell)
%o A066490 a066490 n = a066490_list !! (n-1)
%o A066490 a066490_list = scanl1 (+) $ map a079261 [1..]
%o A066490 -- _Reinhard Zumkeller_, Feb 06 2014
%Y A066490 Cf. A000720, A066339, A296020.
%K A066490 easy,nonn
%O A066490 1,7
%A A066490 _Robert G. Wilson v_, Jan 03 2002