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 A014491 #33 Nov 21 2024 05:12:52
%S A014491 1,1,1,1,1,3,1,1,1,1,1,3,1,1,1,1,1,9,1,5,7,1,1,3,1,1,1,1,1,3,1,1,1,1,
%T A014491 1,9,1,1,1,5,1,21,1,1,1,1,1,3,1,1,1,1,1,27,1,1,1,1,1,15,1,1,7,1,1,3,1,
%U A014491 1,1,1,1,9,1,1,1,1,1,3,1,5,1,1,1,21,1,1,1,1,1,9,1,1,1,1,1,3,1,1
%N A014491 a(n) = gcd(n, 2^n - 1).
%C A014491 Also the GCD of the "binary n-th powers", the set of positive integers whose base-2 representation consists of a block of bits repeated n times consecutively. - _Jeffrey Shallit_, Jan 16 2018
%C A014491 prime(k) for k >= 2 divides a(n) if and only if n is divisible by prime(k)*A014664(k). - _Robert Israel_, Jan 16 2018
%H A014491 T. D. Noe, <a href="/A014491/b014491.txt">Table of n, a(n) for n = 1..10000</a>
%H A014491 Daniel M. Kane, Carlo Sanna, and Jeffrey Shallit, <a href="https://arxiv.org/abs/1801.04483">Waring's theorem for binary powers</a>, arXiv:1801.04483 [math.NT], Jan 13 2018.
%p A014491 A014491:=n->igcd(n, 2^n-1); seq(A014491(n), n=1..100); # _Wesley Ivan Hurt_, Feb 02 2014
%t A014491 Table[GCD[n, 2^n-1], {n, 100}] (* _Harvey P. Dale_, Mar 14 2013 *)
%o A014491 (PARI) a(n) = gcd(n, -1 + 1 << n); \\ _Amiram Eldar_, Nov 21 2024
%Y A014491 Cf. A014664.
%K A014491 nonn,easy,nice
%O A014491 1,6
%A A014491 Gary M. Mcguire (gmm8n(AT)weyl.math.virginia.edu)