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 A369404 #20 Mar 04 2024 00:54:00
%S A369404 8,1,17,19,53,91,197,379,773,1531,3077,6139,12293,24571,49157,98299,
%T A369404 196613,393211,786437,1572859,3145733,6291451,12582917,25165819,
%U A369404 50331653,100663291,201326597,402653179,805306373,1610612731,3221225477,6442450939,12884901893
%N A369404 a(n) = 3*2^n + 5*(-1)^n.
%H A369404 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (1, 2).
%F A369404 a(n) = 3*A000079(n) + 5*A033999(n).
%F A369404 a(n) = 4*A014551(n) - 3*A001045(n).
%F A369404 a(n) = a(n-1) + 2*a(n-2).
%F A369404 G.f.: (8 - 7*x)/((1 + x)*(1 - 2*x)).
%t A369404 LinearRecurrence[{1,2},{8,1},33] (* _James C. McMahon_, Jan 31 2024 *)
%o A369404 (Python)
%o A369404 def A369404(n): return (3<<n)+(-5 if n&1 else 5) # _Chai Wah Wu_, Feb 25 2024
%Y A369404 Cf. A000079, A001045, A014551, A033999.
%K A369404 nonn,easy
%O A369404 0,1
%A A369404 _Philippe Deléham_, Jan 22 2024