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 A083040 #36 Dec 14 2023 05:22:13 %S A083040 1,2,2,3,1,3,1,3,2,2,1,4,1,2,2,3,1,3,1,3,2,2,1,4,1,2,2,3,1,3,1,3,2,2, %T A083040 1,4,1,2,2,3,1,3,1,3,2,2,1,4,1,2,2,3,1,3,1,3,2,2,1,4,1,2,2,3,1,3,1,3, %U A083040 2,2,1,4 %N A083040 Number of divisors of n that are <= 4. %C A083040 Periodic of period 12. Parker vector of the wreath product of S_4 and S, the symmetric group of a countable set. %H A083040 D. A. Gewurz and F. Merola, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL6/Gewurz/gewurz5.html">Sequences realized as Parker vectors of oligomorphic permutation groups</a>, J. Integer Seq., 6 (2003), 03.1.6 %H A083040 <a href="/index/Tu#2wis">Index entries for two-way infinite sequences</a> %H A083040 <a href="/index/Rec#order_12">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,0,0,0,1). %F A083040 G.f.: x/(1-x)+x^2/(1-x^2)+x^3/(1-x^3)+x^4/(1-x^4). %F A083040 a(n) = a(n-12) = a(-n). %F A083040 a(n) = 25/12 - (3/4)*( - 1)^n - 1/2*sin(Pi*n/2) - (1/3)*cos(2*Pi*n/3) - (1/3)*3^(1/2)*sin(2*Pi*n/3) [From _Richard Choulet_, Dec 12 2008] %F A083040 a(n) = sum(k=1..1, cos(n*(k - 1)/1*2*Pi)/1) + sum(k=1..2, cos(n*(k - 1)/2*2*Pi)/2) + sum(k=1..3, cos(n*(k - 1)/3*2*Pi)/3) + sum(k=1..4, cos(n*(k - 1)/4*2*Pi)/4). - _Mats Granvik_, Sep 09 2012 %Y A083040 Cf. A083039, A000005 %K A083040 easy,nonn %O A083040 1,2 %A A083040 Daniele A. Gewurz (gewurz(AT)mat.uniroma1.it) and Francesca Merola (merola(AT)mat.uniroma1.it), May 06 2003