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 A138893 #12 Jun 28 2025 17:54:57
%S A138893 0,11,36,29,8,47,100,65,16,83,164,101,24,119,228,137,32,155,292,173,
%T A138893 40,191,356,209,48,227,420,245,56,263,484,281,64,299,548,317,72,335,
%U A138893 612,353,80,371,676,389,88,407,740,425,96,443,804,461,104,479,868,497
%N A138893 A generalized Chamberland function.
%C A138893 The orbit of a(n) beginning at 1 is A138894.
%D A138893 M. Chamberland, A Continuous Extension of the 3x+1 Problem to the Real Line, Dynamics of Continuous, Discrete and Impulsive Dynamical Systems 2(1996), 495-509.
%H A138893 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2,-3,4,-3,2,-1).
%F A138893 G.f.: x(11+14x-10x^2+14x^3+7x^4)/((1-x)^2(1+x^2)^2);
%F A138893 a(n) = 9n+2-(7n+2)cos(Pi*n/2);
%F A138893 a(n) = 6*((n/3)*(cos(Pi*n/4))^2+(2/3)*(4n+1)*(sin(Pi*n/4))^2);
%F A138893 a(4n) = 8n; a(4n+1) = 11+36n; a(4n+2) = 4*(9+16n); a(4n+3) = 29+36n;
%t A138893 LinearRecurrence[{2,-3,4,-3,2,-1},{0, 11, 36, 29, 8, 47},56] (* or *) CoefficientList[Series[x(11+14x-10x^2+14x^3+7x^4)/((1-x)^2(1+x^2)^2),{x,0,55}],x] (* _James C. McMahon_, Jun 24 2025 *)
%Y A138893 Cf. A138894.
%K A138893 easy,nonn
%O A138893 0,2
%A A138893 _Paul Barry_, Apr 02 2008
%E A138893 a(47)-a(55) from _James C. McMahon_, Jun 24 2025