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 A099430 #16 Jan 08 2025 10:11:13
%S A099430 1,0,4,6,16,30,64,126,256,510,1024,2046,4096,8190,16384,32766,65536,
%T A099430 131070,262144,524286,1048576,2097150,4194304,8388606,16777216,
%U A099430 33554430,67108864,134217726,268435456,536870910,1073741824,2147483646
%N A099430 a(n) = 2^n+(-1)^n-1.
%C A099430 Jacobsthal-Lucas numbers less 1.
%C A099430 For n >= 1, a(n) is also the number of periodic points of period n of the Period Doubling and the Thue-Morse Chain. [Natascha Neumaerker (naneumae(AT)math.uni-bielefeld.de), Apr 06 2009]
%H A099430 N. Neumarker, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL12/Neumarker/neumarker3.html">Realizability of Integer Sequences as Differences of Fixed Point Count Sequences</a>, JIS 12 (2009) 09.4.5, Example 9.
%H A099430 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-2).
%F A099430 G.f.: (1-2x+3x^2)/((1-x)(1-x-2x^2)) = (1-2x+3x^2)/((1-x^2)(1-2x)).
%F A099430 a(n) = A014551(n)-1.
%F A099430 zeta(z) = (1-z)/((1+z)(1-2z)). [Natascha Neumaerker (naneumae(AT)math.uni-bielefeld.de), Apr 06 2009]
%F A099430 a(n) = 2*a(n-1)+a(n-2)-2*a(n-3). - _Wesley Ivan Hurt_, Jun 09 2023
%t A099430 LinearRecurrence[{2,1,-2},{1,0,4},40] (* _Harvey P. Dale_, Nov 07 2017 *)
%o A099430 (PARI) a(n)=2^n+(-1)^n-1 \\ _Charles R Greathouse IV_, May 09 2016
%Y A099430 Cf. A014551.
%K A099430 easy,nonn
%O A099430 0,3
%A A099430 _Paul Barry_, Oct 15 2004