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 A085004 #12 Feb 15 2013 11:54:45 %S A085004 1,2,1,0,-1,0,1,0,-1,-2,-1,0,1,0,-1,0,1,2,1,0,1,2,3,2,1,0,1,2,1,0,-1, %T A085004 0,1,2,1,0,1,2,3,2,1,2,3,4,3,2,1,2,3,2,1,0,1,2,1,0,-1,0,1,2,1,0,1,2,3, %U A085004 2,1,0,1,2,1,0,-1,0,1,0,-1,-2,-1,0,1,0,-1,0,1,2,1,0,-1,0,1,0,-1,-2,-1,0,-1,-2,-3,-2,-1,0,-1,-2,-1,0,1,0,-1,0,1,2,1,0,-1 %N A085004 a(n)=2*A085003(n)-n. %F A085004 |a(n+1)-a(n)| = 1. - _Charles R Greathouse IV_, Feb 07 2013 %o A085004 (PARI) 2*sum(k=1, n, (k+sqrtint(5*k^2))%4>1)-n \\ _Charles R Greathouse IV_, Feb 07 2013 %Y A085004 Cf. A083035, A083036, A083037, A083038, A085003, A085005. %K A085004 sign %O A085004 1,2 %A A085004 _Benoit Cloitre_, Jun 17 2003