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 A247281 #33 Jun 29 2023 11:29:53
%S A247281 0,5,15,65,255,1025,4095,16385,65535,262145,1048575,4194305,16777215,
%T A247281 67108865,268435455,1073741825,4294967295,17179869185,68719476735,
%U A247281 274877906945,1099511627775,4398046511105,17592186044415
%N A247281 a(n) = 4^n -(-1)^n.
%H A247281 OEIS Wiki, <a href="https://oeis.org/wiki/Autosequence">Autosequence</a>
%H A247281 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,4).
%F A247281 a(n) = 5*A015521(n).
%F A247281 a(n+1) = 10*A037481(n) + 5.
%F A247281 a(n+1) = 4*a(n) + 5*(-1)^n.
%F A247281 a(n) = 3*a(n-1) + 4*a(n-2). - _Colin Barker_, Sep 11 2014
%F A247281 G.f.: -5*x / ((x+1)*(4*x-1)). - _Colin Barker_, Sep 11 2014
%t A247281 LinearRecurrence[{3, 4}, {0, 5}, 23] (* _Jean-François Alcover_, May 22 2016 *)
%o A247281 (PARI) concat(0, Vec(-5*x / ((x+1)*(4*x-1)) + O(x^100))) \\ _Colin Barker_, Sep 11 2014
%o A247281 (PARI) vector(100,n,4^(n-1)+(-1)^n) \\ _Derek Orr_, Sep 11 2014
%o A247281 (Python)
%o A247281 def A247281(n): return (1<<(n<<1))+(1 if n&1 else -1) # _Chai Wah Wu_, Jun 28 2023
%Y A247281 Cf. A015521, A037481, A084623.
%K A247281 nonn,easy,less
%O A247281 0,2
%A A247281 _Paul Curtz_, Sep 11 2014
%E A247281 Typos in data fixed by _Colin Barker_, Sep 11 2014