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 A101691 #12 Aug 01 2025 00:11:51
%S A101691 1,1,2,1,3,1,2,2,5,1,2,2,4,2,4,4,9,1,2,2,4,2,4,4,8,2,4,4,8,4,8,8,17,1,
%T A101691 2,2,4,2,4,4,8,2,4,4,8,4,8,8,16,2,4,4,8,4,8,8,16,4,8,8,16,8,16,16,33,
%U A101691 1,2,2,4,2,4,4,8,2,4,4,8,4,8,8,16,2,4,4,8,4,8,8,16,4,8,8
%N A101691 A modular binomial sum sequence.
%H A101691 Harvey P. Dale, <a href="/A101691/b101691.txt">Table of n, a(n) for n = 0..1000</a>
%F A101691 a(n) = Sum_{k=0..n} mod(binomial(2n-2, k), 2).
%F A101691 a(2^n) = A094373(n). a(2^n-1) = 1,1,1,2,4,8,16,...
%t A101691 Table[Sum[Mod[Binomial[2n-2,k],2],{k,0,n}],{n,0,100}] (* _Harvey P. Dale_, Oct 20 2011 *)
%o A101691 (Python)
%o A101691 def A101691(n): return sum((not ~(n-1<<1)&k) for k in range(n+1)) # _Chai Wah Wu_, Jul 31 2025
%Y A101691 Cf. A048896.
%K A101691 easy,nonn
%O A101691 0,3
%A A101691 _Paul Barry_, Dec 11 2004