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 A196686 #31 Feb 23 2025 11:44:58
%S A196686 1,2,1,2,3,4,3,2,3,4,5,4,5,6,7,8,7,8,7,6,5,4,3,2,3,4,3,4,3,4,5,6,5,4,
%T A196686 3,2,1,2,3,4,5,4,5,6,7,8,9,10,11,12,11,12,11,10,9,10,11,10,11,10,9,10,
%U A196686 11,10,11,10,11,10,11,10,9,8,7,6,5,4,3,2,1,2,3,2,1,0,-1,-2,-1,-2,-3,-4,-3,-2,-3,-4,-3,-2
%N A196686 Number of odd digits of Pi minus number of even digits.
%C A196686 Cumulative sum of A030657 with zeros replaced by "-1".
%H A196686 Zak Seidov, <a href="/A196686/b196686.txt">Table of n, a(n) for n = 1..10000</a> [a(10000) corrected by _Georg Fischer_, Dec 29 2021]
%H A196686 Zak Seidov, <a href="https://oeis.org/wiki/File:A196686Fig1.jpg">Dependence a(n) for n = 1..10000</a>
%H A196686 Zak Seidov, <a href="https://oeis.org/wiki/File:A196686Fig2.jpg">Dependence a(n) for n = 1..10^6</a>
%e A196686 Among first 10 digits of Pi, {3,1,4,1,5,9,2,6,5,3}, there are 7 odd and 3 even, hence a(10)=7-3=4.
%t A196686 rd=RealDigits[N[Pi, 10004]][[1]]; a=0; s=Reap[Do[a=a+2Mod[rd[[n]],2]-1; Sow[{n,a}], {n,10004}]][[2,1]] (* this gives b-file *) (* _Zak Seidov_, Oct 05 2011 *)
%t A196686 Module[{nn=100,pid},pid=RealDigits[Pi,10,nn][[1]];Accumulate[If[OddQ[#],1,-1]&/@pid]] (* _Harvey P. Dale_, Feb 23 2025 *)
%Y A196686 Cf. A030657, A175792 (negated), A175813 (indices of 0's).
%K A196686 sign,base
%O A196686 1,2
%A A196686 _Zak Seidov_, Oct 05 2011
%E A196686 Definition amended by _Georg Fischer_, Dec 29 2021