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 A101680 #12 Aug 01 2025 11:09:30
%S A101680 1,11,111,1011,10111,111011,1100111,10001011,100010111,1100111011,
%T A101680 11101100111,101110001011,1011000010111,11100000111011,
%U A101680 110000001100111,1000000010001011,10000000100010111,110000001100111011,1110000011101100111,10110000101110001011,101110001011000010111
%N A101680 A modular binomial transform of 10^n.
%F A101680 a(n) = Sum{k=0..n} mod(binomial(2n-k, k), 2)*10^k<;
%o A101680 (Python)
%o A101680 def A101680(n): return sum(int(not ~((n<<1)-k)&k)*10**k for k in range(n+1)) # _Chai Wah Wu_, Jul 30 2025
%o A101680 (PARI) a(n) = sum(k=0, n, lift(Mod(binomial(2*n-k, k), 2))*10^k); \\ _Michel Marcus_, Jul 31 2025
%Y A101680 A099902 in binary. Bisection of A101623.
%K A101680 easy,nonn
%O A101680 0,2
%A A101680 _Paul Barry_, Dec 11 2004
%E A101680 More terms from _Michel Marcus_, Jul 31 2025