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 A168570 #19 Mar 27 2017 10:58:12
%S A168570 0,1,0,1,0,2,0,1,0,1,0,2,0,1,0,1,0,3,0,1,0,1,0,2,0,1,0,1,0,2,0,1,0,1,
%T A168570 0,3,0,1,0,1,0,2,0,1,0,1,0,2,0,1,0,1,0,4,0,1,0,1,0,2,0,1,0,1,0,2,0,1,
%U A168570 0,1,0,3,0,1,0,1,0,2,0,1,0,1,0,2,0,1,0,1,0,3,0,1,0,1,0,2,0,1,0,1,0,2,0,1,0
%N A168570 Exponent of 3 in 2^n - 1.
%C A168570 Records: a(A025192(n)) = n and a(k) < n for k < A025192(n). [_Joerg Arndt_, Apr 07 2014]
%H A168570 T. D. Noe, <a href="/A168570/b168570.txt">Table of n, a(n) for n = 1..10000</a>
%e A168570 For n=6, 2^6 - 1 = 63. Greatest divisor of 63 which is a power of 3 is 9 (3^2).
%p A168570 a:= n-> padic[ordp](2^n-1, 3):
%p A168570 seq(a(n), n=1..120); # _Alois P. Heinz_, Mar 27 2017
%t A168570 Table[IntegerExponent[2^n - 1, 3], {n, 100}] (* _T. D. Noe_, Apr 13 2014 *)
%o A168570 (PARI) vector(100,n,valuation(2^n-1,3)) /* _Joerg Arndt_, Jun 13 2011 */
%Y A168570 Cf. A051064 (without the zeros).
%K A168570 nonn
%O A168570 1,6
%A A168570 _Martins Opmanis_, Nov 30 2009