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 A101836 #14 Feb 09 2021 02:37:46
%S A101836 0,0,1,2,5,12,25,50,99,198,400,803,1605,3210,6422,12848,25692,51384,
%T A101836 102784,205563,411115,822234,1644470,3288958,6577915,13155768,
%U A101836 26311537,52623102,105246259,210492628,420985102,841970065,1683940202,3367880511,6735761133,13471522233
%N A101836 a(n) = 2^n - A143658(n).
%C A101836 The number of integers not exceeding 2^n that are not squarefree.
%H A101836 Amiram Eldar, <a href="/A101836/b101836.txt">Table of n, a(n) for n = 0..64</a> (calculated from the b-file at A143658)
%t A101836 c = 0; k = 1; lst = {}; Do[ While[k <= 2^n, If[ !SquareFreeQ@ k, c++ ]; k++ ]; AppendTo[lst, c], {n, 0, 26}]; lst
%Y A101836 Cf. A013929, A143658.
%K A101836 nonn
%O A101836 0,4
%A A101836 _Robert G. Wilson v_, Aug 31 2008
%E A101836 a(0) inserted and more terms added by _Amiram Eldar_, Feb 09 2021