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 A065357 #26 Jun 18 2018 11:44:39
%S A065357 1,1,-1,1,1,-1,-1,1,1,1,1,-1,-1,1,1,1,1,-1,-1,1,1,1,1,-1,-1,-1,-1,-1,
%T A065357 -1,1,1,-1,-1,-1,-1,-1,-1,1,1,1,1,-1,-1,1,1,1,1,-1,-1,-1,-1,-1,-1,1,1,
%U A065357 1,1,1,1,-1,-1,1,1,1,1,1,1,-1,-1,-1,-1,1,1,-1,-1,-1,-1,-1,-1,1,1,1,1,-1,-1,-1,-1,-1,-1,1,1,1,1,1,1,1,1,-1,-1,-1,-1,1,1
%N A065357 a(n) = (-1)^pi(n) where pi(n) is the number of primes <= n.
%H A065357 N. J. A. Sloane, <a href="/A065357/b065357.txt">Table of n, a(n) for n = 0..10000</a> (First 1000 terms from Harry J. Smith)
%t A065357 (-1)^PrimePi[Range[0,110]] (* _Harvey P. Dale_, Nov 02 2015 *)
%o A065357 (PARI) { for (n=0, 1000, if (n, a=(-1)^primepi(n), a=1); write("b065357.txt", n, " ", a) ) } \\ _Harry J. Smith_, Sep 30 2009
%Y A065357 Cf. A000720, A065358.
%K A065357 easy,sign
%O A065357 0,1
%A A065357 _Jason Earls_, Oct 31 2001