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 A380384 #23 Feb 05 2025 22:25:42
%S A380384 0,1,3,9,21,47,99,205,417,843,1695,3401,6813,13639,27291,54597,109209,
%T A380384 218435,436887,873793,1747605,3495231,6990483,13980989,27962001,
%U A380384 55924027,111848079,223696185,447392397,894784823,1789569675,3579139381,7158278793,14316557619
%N A380384 a(0)=0, a(n) = 2*(a(n-1) + ceiling(n/2)) - 1 for n>0.
%H A380384 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,-1,-3,2).
%F A380384 G.f.: x*(x^2+1)/((x+1)*(1-2*x)*(x-1)^2).
%F A380384 a(n) = floor(2^n*5/3) - n - 1.
%F A380384 a(n) = A081254(n+1) - n - 1.
%F A380384 a(n) = a(n-4) + A250777(n-3).
%t A380384 LinearRecurrence[{3, -1, -3, 2}, {0, 1, 3, 9}, 40] (* _Amiram Eldar_, Jan 24 2025 *)
%Y A380384 Cf. A081254, A109613, A250777.
%K A380384 nonn,easy
%O A380384 0,3
%A A380384 _Paul Curtz_, Jan 23 2025