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 A166871 #12 May 28 2016 04:16:45
%S A166871 0,1,2,3,-1,-2,4,5,6,-3,-4,7,8,9,-5,-6,10,11,12,-7,-8,13,14,15,-9,-10,
%T A166871 16,17,18,-11,-12,19,20,21,-13,-14,22,23,24,-15,-16,25,26,27,-17,-18,
%U A166871 28,29,30,-19,-20,31,32,33,-21,-22,34,35,36,-23,-24,37,38,39,-25,-26,40,41
%N A166871 Permutation of the integers: 3 positives, 2 negatives.
%C A166871 This sequence enumerates the denominators with sign in case p=3 and n=2 of:
%C A166871 log(p/n) = sum( i>=0, sum(p*i+1<=j<=p*(i+1),1/j) - sum(n*i+1<=j<=n*(i+1),1/j) )
%C A166871 Similar sequences can be constructed for the logarithm of any rational r=p/n (p,n>0), enumerating p positive integers and n negative integers every p+n terms.
%C A166871 Case p=2, n=1 is A166711.
%C A166871 Case p=1, n=1 is A001057.
%H A166871 G. C. Greubel, <a href="/A166871/b166871.txt">Table of n, a(n) for n = 0..1000</a>
%H A166871 Wikipedia, <a href="http://en.wikipedia.org/wiki/Riemann_series_theorem">Riemann series theorem</a>
%H A166871 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,2,0,0,0,0,-1)
%F A166871 Sum_{k>0} 1/a(k) = log(3/2).
%F A166871 G.f.: x*(1+2*x+3*x^2-x^3-2*x^4+2*x^5+x^6-x^8)/((x-1)^2*(x^4+x^3+x^2+x+1)^2 ).
%t A166871 LinearRecurrence[{0,0,0,0,2,0,0,0,0,-1},{0,1,2,3,-1,-2,4,5,6,-3}, 100] (* _G. C. Greubel_, May 27 2016 *)
%Y A166871 Cf. A016578, A166711.
%K A166871 sign,easy
%O A166871 0,3
%A A166871 _Jaume Oliver Lafont_, Oct 22 2009
%E A166871 keyword frac removed _Jaume Oliver Lafont_, Nov 02 2009